MCA Doppler study
Middle Cerebral Artery (MCA) Fetal doppler & normal value
Normal Value
Middle Cerebral Artery (MCA) Doppler
Middle Cerebral Artery (MCA) Doppler assesses fetal cerebral circulation and oxygenation status by evaluating blood flow velocity waveforms in the middle cerebral artery. It reflects cerebral vascular resistance and perfusion. As gestation advances, cerebral vascular resistance decreases, and diastolic flow increases. In response to fetal hypoxia or anemia, the cerebral arteries undergo vasodilation, reducing resistance—a protective mechanism termed the "brain-sparing effect." Abnormally low MCA resistance (high diastolic flow) can indicate fetal anemia, hypoxia, or intrauterine growth restriction (IUGR) with redistribution of cardiac output to vital organs.
S/D ratio → S/D ratio (Systolic/Diastolic ratio) is the ratio of peak systolic velocity (S) to end-diastolic velocity (D) in the middle cerebral artery waveform. It is one of the most commonly used Doppler indices to assess cerebral perfusion and detect fetal compromise.
Formula:
S/D ratio = Peak Systolic Velocity (S) ÷ End-Diastolic Velocity (D)
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. Under normal conditions, the brain receives a relatively high-resistance blood supply proportional to body oxygenation. When the fetus becomes hypoxic or anemic, the cerebral vasculature undergoes vasodilation to increase cerebral perfusion—the diastolic flow increases sharply, and the S/D ratio decreases. Conversely, normal or elevated resistance indicates adequate fetal oxygenation.
As gestation advances from 20 to 40 weeks, the cerebral circulation matures, vascular resistance gradually falls, diastolic flow increases, and the S/D ratio progressively decreases.
• 20 weeks: ~4.5–5.0 (high resistance, developing circulation)
• 28 weeks: ~3.5–4.0 (resistance falling)
• 34 weeks: ~2.8–3.2
Measuring technique for S/D:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA with angle of insonation close to 0°.
4. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
5. On each waveform, mark the peak systolic point (S) and the end-diastolic point (D).
6. Most ultrasound machines auto-calculate the S/D ratio; take the mean of 3 waveforms for reporting.
7. Angle correction is not required for ratio-based indices (S/D, RI, PI), as both numerator and denominator are equally affected by the angle.
Normal S/D Ratio Reference Values for MCA by Gestational Age
Abnormal patterns:
• S/D < 5th centile for GA → Reduced cerebral vascular resistance; increased diastolic flow. Indicates cerebral vasodilation in response to hypoxia or anemia. Brain-sparing effect.
• S/D > 95th centile for GA → Elevated cerebral vascular resistance; decreased diastolic flow. Indicates inadequate cerebral vascular maturation or primary cerebral compromise.
• Persistently elevated S/D beyond expected GA → Delayed cerebral vascular maturation; may indicate IUGR, fetal growth restriction, or placental insufficiency with inadequate fetal adaptation.
• Rapidly declining S/D across serial scans → Progressive cerebral vasodilation; suggests worsening fetal hypoxia or development of anemia.
Limitation of S/D ratio:
The S/D ratio is a simple but crude measure of cerebral vascular resistance. It is angle-dependent and becomes unreliable when end-diastolic flow is very low or nearly absent. In situations requiring more precise hemodynamic assessment, the Pulsatility Index (PI) and Resistance Index (RI) are preferred, as they normalize the measurement and are less susceptible to angle variations and flow characteristics. PI and RI remain mathematically valid across the full range of resistance states.
Clinical Decision Thresholds (MCA S/D Ratio)
Key points to remember:
• MCA S/D ratio decreases with advancing gestation (normal trend from ~4.5 at 20 weeks to ~2.3 at 40 weeks).
• A rising or static MCA S/D ratio across serial scans is concerning even if still within "normal" range — suggests failing compensatory mechanism.
• Always interpret MCA S/D ratio against gestational-age-specific centiles, not a single cut-off value.
• Low MCA S/D ratio (brain-sparing effect) should be correlated with elevated UA S/D ratio (placental insufficiency) for complete picture.
• MCA S/D ratio is angle-dependent — maintain consistent angle of insonation (close to 0°) for reproducible measurements.
• Measure on the M1 segment of MCA, proximal to branching, to avoid measurement artifacts and ensure consistency.
• MCA S/D, RI, and PI are correlated; most centres now report PI as the primary parameter, with S/D as supportive.
• Combine MCA and UA Doppler assessment for comprehensive evaluation: elevated UA resistance + reduced MCA resistance = severe placental insufficiency with brain-sparing effect.
RI (Resistance Index) → RI (Resistance Index) is a normalized Doppler index that reflects vascular resistance in the middle cerebral artery. It is calculated from peak systolic velocity (S) and end-diastolic velocity (D), and is independent of angle of insonation, making it highly reproducible and reliable.
Formula:
RI = (Peak Systolic Velocity - End-Diastolic Velocity) ÷ Peak Systolic Velocity
RI = (S - D) ÷ S
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. Under normal conditions, the brain receives a relatively high-resistance blood supply proportional to body oxygenation. When the fetus becomes hypoxic or anemic, the cerebral vasculature undergoes vasodilation to increase cerebral perfusion—the diastolic flow increases sharply, and the RI decreases. Conversely, normal or elevated resistance indicates adequate fetal oxygenation.
As gestation advances from 20 to 40 weeks, the cerebral circulation matures, vascular resistance gradually falls, diastolic flow increases, and the RI progressively decreases.
• 20 weeks: ~0.82–0.88 (high resistance, developing circulation)
• 28 weeks: ~0.70–0.78 (resistance falling)
• 34 weeks: ~0.62–0.70
Measuring technique for RI:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA with angle of insonation close to 0°.
4. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
5. On each waveform, mark the peak systolic point (S) and the end-diastolic point (D).
6. Most ultrasound machines auto-calculate the RI; take the mean of 3 waveforms for reporting.
7. RI is angle-independent and provides more reliable assessment across different insonation angles compared to S/D ratio.
Normal RI Reference Values for MCA by Gestational Age
Abnormal patterns:
• RI < 5th centile for GA → Reduced cerebral vascular resistance; increased diastolic flow. Indicates cerebral vasodilation in response to hypoxia or anemia. Brain-sparing effect.
• RI > 95th centile for GA → Elevated cerebral vascular resistance; decreased diastolic flow. Indicates inadequate cerebral vascular maturation or primary cerebral compromise.
• Persistently elevated RI beyond expected GA → Delayed cerebral vascular maturation; may indicate IUGR, fetal growth restriction, or placental insufficiency with inadequate fetal adaptation.
• Rapidly declining RI across serial scans → Progressive cerebral vasodilation; suggests worsening fetal hypoxia or development of anemia.
• Rising or static RI on serial scans → Increasing cerebral resistance; indicates deteriorating fetal status or failed compensatory mechanism.
Advantages of RI over S/D ratio:
The RI is a normalized index that is independent of angle of insonation, making it more reproducible and reliable than S/D ratio across different measurement angles. RI normalizes the relationship between systolic and diastolic velocities and remains mathematically valid even when end-diastolic flow is very low (approaching zero), whereas S/D ratio becomes extremely large or undefined. RI is therefore superior for detecting subtle changes in cerebral resistance and for tracking serial changes over time.
Clinical Decision Thresholds (MCA RI)
RI value patterns and their clinical significance:
Cerebroplacental Ratio (CPR): CPR = MCA RI ÷ UA RI
• Normal CPR (≥ 1.0 at term): MCA resistance lower than or equal to UA resistance; normal placental-cerebral relationship
• Abnormal CPR (< 1.0 at term): MCA resistance higher than UA resistance; indicates failed brain-sparing effect; associated with worse outcomes
• Markedly reduced MCA RI with elevated UA RI: Severe placental insufficiency with appropriate brain-sparing compensation; imminent fetal decompensation risk
Serial RI assessment:
• Stable RI within normal range: Reassuring; continue routine surveillance
• RI declining (improving): Normal vascular maturation; favorable sign
• RI static or rising: Concerning pattern; suggests failure of normal maturation or progressive compromise
• Rapid changes in RI: Indicates acute hemodynamic shifts; requires urgent evaluation and intervention planning
Key points to remember:
• MCA RI decreases with advancing gestation (normal trend from ~0.85 at 20 weeks to ~0.65 at 40 weeks).
• A rising or static MCA RI across serial scans is concerning and indicates abnormal resistance progression.
• Always interpret MCA RI against gestational-age-specific centiles, not a single cut-off value.
• Low MCA RI (brain-sparing effect) should be correlated with elevated UA RI (placental insufficiency) for complete assessment.
• MCA RI is angle-independent — more reproducible than S/D ratio; allows reliable serial comparisons even with slight angle variations.
• Measure on the M1 segment of MCA, proximal to branching, to ensure consistent measurements.
• Combine MCA and UA RI assessment — calculate Cerebroplacental Ratio (CPR) for comprehensive evaluation of fetal hemodynamic status.
• CPR < 1.0 at term is abnormal and indicates failure of brain-sparing compensation; associated with increased perinatal mortality.
• MCA RI, S/D, and PI are correlated; RI provides normalized, angle-independent assessment superior to S/D for detecting subtle changes.
• Consider umbilical artery (UA) RI, middle cerebral artery (MCA) RI, and cerebroplacental ratio (CPR) as the foundation of Doppler assessment in high-risk pregnancies.
PI (Pulsatility Index) → PI (Pulsatility Index) is a normalized Doppler index that reflects vascular resistance and compliance in the middle cerebral artery. It is calculated from peak systolic velocity (S), end-diastolic velocity (D), and mean velocity (M), and is independent of angle of insonation, making it highly reproducible and reliable for assessing fetal cerebral perfusion.
Formula:
PI = (Peak Systolic Velocity - End-Diastolic Velocity) ÷ Mean Velocity
PI = (S - D) ÷ M
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. Under normal conditions, the brain receives a relatively high-resistance blood supply proportional to body oxygenation. When the fetus becomes hypoxic or anemic, the cerebral vasculature undergoes vasodilation to increase cerebral perfusion—the diastolic flow increases sharply, and the PI decreases. Conversely, normal or elevated resistance indicates adequate fetal oxygenation.
As gestation advances from 20 to 40 weeks, the cerebral circulation matures, vascular resistance gradually falls, diastolic flow increases, and the PI progressively decreases. PI is considered more sensitive than RI and S/D ratio for detecting subtle changes in cerebral hemodynamics.
• 20 weeks: ~2.0–2.3 (high resistance, developing circulation)
• 28 weeks: ~1.5–1.8 (resistance falling)
• 34 weeks: ~1.2–1.5
Measuring technique for PI:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA with angle of insonation close to 0°.
4. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
5. On each waveform, identify the peak systolic point (S), end-diastolic point (D), and calculate or identify the mean velocity (M).
6. Most ultrasound machines auto-calculate the PI; take the mean of 3 waveforms for reporting.
7. PI is angle-independent and provides superior assessment of vascular resistance and compliance compared to S/D ratio and RI.
Normal PI Reference Values for MCA by Gestational Age
Abnormal patterns:
• PI < 5th centile for GA → Reduced cerebral vascular resistance; increased diastolic flow. Indicates cerebral vasodilation in response to hypoxia or anemia. Brain-sparing effect.
• PI > 95th centile for GA → Elevated cerebral vascular resistance; decreased diastolic flow. Indicates inadequate cerebral vascular maturation or primary cerebral compromise.
• Persistently elevated PI beyond expected GA → Delayed cerebral vascular maturation; may indicate IUGR, fetal growth restriction, or placental insufficiency with inadequate fetal adaptation.
• Rapidly declining PI across serial scans → Progressive cerebral vasodilation; suggests worsening fetal hypoxia or development of anemia.
• Rising or static PI on serial scans → Increasing cerebral resistance; indicates deteriorating fetal status or failed compensatory mechanism.
Advantages of PI over S/D ratio and RI:
The PI is considered the gold standard Doppler index for cerebral vascular resistance assessment because it is completely independent of angle of insonation and incorporates mean velocity in its calculation. PI is the most sensitive for detecting subtle hemodynamic changes and provides superior discrimination between normal and abnormal resistance states. Unlike S/D ratio, PI remains mathematically valid even when end-diastolic flow is extremely low or nearly absent. PI is more robust for serial comparisons and is the preferred primary parameter in most fetal medicine centres for comprehensive hemodynamic evaluation.
Clinical Decision Thresholds (MCA PI)
PI value patterns and their clinical significance:
Cerebroplacental Ratio using PI (PI-CPR): PI-CPR = MCA PI ÷ UA PI
• Normal PI-CPR (≥ 1.0 at term): MCA resistance lower than or equal to UA resistance; normal placental-cerebral relationship; appropriate brain perfusion
• Abnormal PI-CPR (< 1.0 at term): MCA resistance higher than UA resistance; indicates failed brain-sparing effect; associated with worse perinatal outcomes
• Markedly reduced MCA PI with elevated UA PI: Severe placental insufficiency with appropriate brain-sparing compensation; indicates significant fetal compromise
• PI-CPR < 0.9 at term: High risk for adverse outcome; consider delivery planning
Serial PI assessment and trend analysis:
• Stable PI within normal range: Reassuring; continue routine surveillance
• PI declining (improving): Normal vascular maturation; favorable sign; expected pattern
• PI static or rising: Concerning pattern; suggests failure of normal maturation or progressive compromise
• Rapid changes in PI (>0.2 unit change): Indicates acute hemodynamic shifts; requires urgent evaluation and immediate intervention planning
• Crossing centile lines downward: Reassuring progression; normal maturation
• Crossing centile lines upward: Concerning; indicates abnormal resistance increase; requires urgent assessment
PI-guided clinical management thresholds:
At ≥34 weeks gestation:
• MCA PI > 95th centile + abnormal UA Doppler → Consider delivery
• MCA PI < 5th centile + elevated UA PI → Consider delivery
• PI-CPR < 1.0 + other concerning features → Delivery recommended
At 32–33 weeks gestation:
• MCA PI < 5th centile + UA RI > 95th centile → Daily CTG; consider delivery if other signs of compromise present
• Progressive worsening of PI on serial scans → Intensive surveillance; prepare for emergency delivery
Key points to remember:
• MCA PI decreases with advancing gestation (normal trend from ~2.0 at 20 weeks to ~1.0 at 40 weeks).
• A rising or static MCA PI across serial scans is concerning and indicates abnormal resistance progression.
• Always interpret MCA PI against gestational-age-specific centiles, not a single cut-off value.
• Low MCA PI (brain-sparing effect) should be correlated with elevated UA PI (placental insufficiency) for complete assessment.
• MCA PI is the most angle-independent and reproducible of all Doppler indices; ideal for serial comparisons over time.
• Measure on the M1 segment of MCA, proximal to branching, to ensure consistent measurements.
• Calculate Cerebroplacental Ratio using PI (PI-CPR = MCA PI ÷ UA PI) for comprehensive evaluation of fetal hemodynamic status.
• PI-CPR < 1.0 at term is abnormal and indicates failure of brain-sparing compensation; associated with increased perinatal morbidity and mortality.
• Trending PI values is more important than absolute values — serial assessment detects progressive changes earlier than isolated measurements.
• MCA PI is the preferred primary Doppler parameter in fetal medicine; S/D and RI are supportive.
• Use MCA PI, UA PI, and PI-CPR as the foundation of Doppler assessment in high-risk pregnancies; supplement with DV Doppler when severe compromise suspected.
PSV (Peak Systolic Velocity) → PSV (Peak Systolic Velocity) is the maximum blood flow velocity during ventricular systole in the middle cerebral artery. Unlike ratio-based indices (S/D, RI, PI), PSV is an absolute velocity measurement that directly reflects blood flow speed and is highly dependent on angle of insonation. PSV is increasingly used to assess fetal anemia and cerebral perfusion in cases of suspected intrauterine growth restriction (IUGR).
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. PSV increases with gestational age due to progressive increase in fetal cardiac output and improved vascular flow. In fetal anemia, the reduced oxygen-carrying capacity of blood triggers compensatory cerebral vasodilation and increased cardiac output, resulting in elevated PSV. An elevated MCA PSV (>1.5 multiples of the median, MoM) is a sensitive marker for detecting moderate-to-severe fetal anemia. Conversely, in severe IUGR with hypoxia, PSV may be low or normal as the fetus attempts to conserve energy.
As gestation advances from 20 to 40 weeks, the fetal heart becomes more efficient, cardiac output increases, and PSV progressively increases. PSV values must be interpreted in the context of gestational age-specific nomograms.
• 20 weeks: ~35–45 cm/s (developing circulation, lower velocities)
• 28 weeks: ~50–65 cm/s (increasing with fetal growth)
• 34 weeks: ~65–80 cm/s
Measuring technique for PSV:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA.
4. Adjust the angle of insonation as close to 0° as possible — angle correction is critical for PSV measurements.
5. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
6. On each waveform, identify the highest peak of the systolic envelope and record the velocity value.
7. Take the mean of 3 measurements for reporting.
8. Always note the angle of insonation used in the report, as small angle variations significantly affect PSV values.
Normal PSV Reference Values for MCA by Gestational Age
Abnormal patterns:
• PSV > 1.5 MoM (multiples of the median) for GA → Elevated peak systolic velocity; indicates increased cerebral blood flow. Highly sensitive for detecting fetal anemia.
• PSV > 1.3 MoM for GA → Borderline elevated; mild anemia or early compensatory response to hypoxia.
• PSV < 5th centile for GA → Reduced peak systolic velocity; indicates decreased cardiac output or severe compromise. May indicate severe IUGR, cardiac dysfunction, or terminal fetal status.
• PSV normal or low with elevated UA PI/RI → Suggests severe IUGR with failed compensatory mechanism; indicates critical fetal status.
• Progressively rising PSV on serial scans → Progressive increase in cerebral blood flow; indicates worsening anemia or hypoxia with increasing compensatory response.
• Rapidly declining PSV on serial scans → Acute decrease in cardiac output; indicates fetal decompensation and critical compromise.
Clinical significance and advantages of PSV:
Unlike ratio-based indices (S/D, RI, PI), PSV is an absolute velocity measurement that directly reflects blood flow speed and cardiac output. PSV is highly sensitive for detecting fetal anemia — a PSV > 1.5 MoM has near-100% sensitivity for moderate-to-severe anemia (hemoglobin < 7 g/dL). PSV assessment is particularly valuable in Rh-alloimmunized pregnancies, fetomaternal hemorrhage, or suspected hemolytic disease where anemia is a primary concern. However, PSV is angle-dependent and requires strict attention to measurement technique. PSV is best used in conjunction with other Doppler parameters (RI, PI, mean velocity) for comprehensive hemodynamic assessment.
Clinical Decision Thresholds (MCA PSV)
PSV measurement and interpretation guidelines:
Measurement technique critical points:
• Angle of insonation: Must be as close to 0° as possible; even 10° angle error can result in 15% error in PSV value.
• Consistent measurement location: Always measure at M1 segment; proximal MCA near Circle of Willis.
• Sample volume placement: Center sample volume in vessel lumen; avoid vessel walls.
• Baseline adjustment: Ensure baseline is set correctly; misalignment causes systematic errors.
Nomogram selection and MoM calculation:
• Use gestational-age-specific nomograms: PSV increases significantly with advancing gestation (35–45 cm/s at 20 weeks to 78–98 cm/s at 40 weeks).
• Calculate MoM (multiples of the median): MoM = Measured PSV ÷ Median PSV for GA.
• MoM approach superior to absolute values: Accounts for normal physiologic variation with gestation; provides standardized interpretation.
• Always report both absolute PSV and MoM in clinical assessment.
PSV in anemia detection:
• PSV > 1.5 MoM: Sensitivity ~100% for moderate-to-severe anemia; specificity ~75–80%
• PSV 1.3–1.5 MoM: Sensitivity lower; overlap between normal and mild anemia; requires clinical correlation
• PSV within normal range does NOT exclude anemia: Mild anemia may not elevate PSV; clinical context essential
• In Rh disease: Serial PSV assessment superior to periodic measurements; rising trend indicates progressive anemia
PSV in IUGR and hypoxia assessment:
• Low PSV with elevated UA PI: Indicates severe IUGR with reduced cardiac output; poor prognosis
• Normal PSV with elevated UA PI: Early IUGR with maintained cardiac compensation; better prognosis
• PSV declining with worsening UA Doppler: Indicates progression to decompensation; imminent delivery needed
PSV-guided clinical management and decision points:
In Rh-alloimmunized pregnancies:
• PSV > 1.5 MoM → Cordocentesis for confirmation of anemia
• Confirmed anemia Hb < 7 g/dL → Intrauterine transfusion (IUT)
• Serial PSV trending → Guides timing of repeat IUT
At ≥34 weeks gestation:
• PSV > 1.5 MoM + confirmed anemia → Delivery recommended
• PSV > 1.8 MoM + signs of cardiac compromise → Immediate delivery
• PSV < 5th centile + abnormal UA Doppler → Delivery recommended
At 32–33 weeks gestation:
• PSV > 1.8 MoM → Urgent assessment; consider delivery if other signs of compromise
• PSV borderline elevated + Rh disease → Cordocentesis for definitive diagnosis
• Progressive PSV rise on serial scans → More frequent monitoring; prepare for intervention
Before 32 weeks gestation:
• PSV > 1.5 MoM in Rh disease → Cordocentesis + consider IUT
• Isolated PSV elevation without other abnormalities → Serial monitoring every 3–5 days
• Progressive rise in PSV → More aggressive intervention planning
Key points to remember:
• MCA PSV increases with advancing gestation (normal trend from ~40 cm/s at 20 weeks to ~85 cm/s at 40 weeks).
• PSV is angle-dependent — maintain angle of insonation <0° and be consistent for reproducible measurements.
• Always use MoM (multiples of median) rather than absolute PSV values; accounts for gestational-age variation.
• PSV > 1.5 MoM has ~100% sensitivity for moderate-to-severe anemia; use for screening in at-risk populations.
• Isolated PSV elevation does not diagnose anemia; requires clinical context and other assessment methods (cordocentesis).
• Measure on the M1 segment of MCA, proximal to branching, maintaining consistent technique.
• Serial PSV assessment superior to single measurements — trending over time detects progressive changes and guides intervention timing.
• Combine PSV with other Doppler parameters (RI, PI, EDV, UA Doppler, DV Doppler) for comprehensive hemodynamic evaluation.
• PSV is particularly valuable in Rh-alloimmunized pregnancies, fetomaternal hemorrhage, and hemolytic disease.
• PSV declining rapidly is alarming — indicates acute decompensation and requires urgent intervention.
• PSV normal or low with abnormal placental Doppler suggests IUGR, not anemia; indicates need for delivery planning.
EDV (End-Diastolic Velocity) → EDV (End-Diastolic Velocity) is the minimum blood flow velocity at the end of ventricular diastole in the middle cerebral artery. Unlike ratio-based indices (S/D, RI, PI), EDV is an absolute velocity measurement that directly reflects the baseline diastolic flow and is highly dependent on angle of insonation. EDV is increasingly used to assess fetal anemia and cerebral perfusion in cases of suspected intrauterine growth restriction (IUGR) and fetal hypoxia.
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. EDV increases with gestational age due to progressive reduction in cerebral vascular resistance and improved forward diastolic flow. In fetal anemia, the reduced oxygen-carrying capacity of blood triggers compensatory cerebral vasodilation and increased cardiac output, resulting in elevated EDV. An elevated MCA EDV reflects increased diastolic flow and is a marker of fetal anemia and increased cerebral perfusion.
Conversely, in severe IUGR with hypoxia and poor cardiac function, EDV may be low or absent as the fetus struggles to maintain adequate perfusion.
As gestation advances from 20 to 40 weeks, the cerebral vascular bed matures, resistance falls, and EDV progressively increases. EDV values must be interpreted in the context of gestational age-specific nomograms and in conjunction with PSV to calculate resistance indices.
• 20 weeks: ~10–15 cm/s (high resistance, minimal diastolic flow)
• 28 weeks: ~20–28 cm/s (diastolic flow improving)
• 34 weeks: ~28–35 cm/s
Measuring technique for EDV:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA.
4. Adjust the angle of insonation as close to 0° as possible — angle correction is critical for EDV measurements.
5. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
6. On each waveform, identify the lowest point of the diastolic envelope (the point just before the next systolic rise) and record the velocity value.
7. Take the mean of 3 measurements for reporting.
8. Always note the angle of insonation used in the report, as small angle variations significantly affect EDV values.
Normal EDV Reference Values for MCA by Gestational Age
Abnormal patterns:
• EDV > 95th centile for GA → Elevated end-diastolic velocity; indicates increased diastolic flow and cerebral vasodilation. Reflects brain-sparing effect in response to hypoxia or anemia.
• EDV < 5th centile for GA → Reduced end-diastolic velocity; indicates decreased diastolic flow and high cerebral vascular resistance. Suggests inadequate cerebral vascular maturation or primary cerebral compromise.
• EDV progressively rising on serial scans → Progressive increase in diastolic flow; indicates worsening anemia or hypoxia with increasing compensatory cerebral vasodilation.
• EDV progressively declining on serial scans → Progressive decrease in diastolic flow; indicates deteriorating cerebral perfusion and increasing vascular resistance.
• Elevated EDV with normal PSV → Unusual pattern; suggests selective diastolic flow increase; evaluate for specific hemodynamic disturbances.
• EDV markedly elevated with elevated PSV → Indicates uniform increase in flow across cardiac cycle; consistent with high-output state (anemia, hypoxia with compensation).
Clinical significance and advantages of EDV:
Unlike ratio-based indices (S/D, RI, PI), EDV is an absolute velocity measurement that directly reflects diastolic cerebral blood flow. EDV is sensitive for detecting cerebral vasodilation that occurs with fetal anemia, hypoxia, and IUGR with brain-sparing effect. Elevated EDV with elevated PSV indicates a high-output compensatory state typical of fetal anemia or acute hypoxia. Conversely, reduced EDV with low PSV indicates low-output failure associated with severe IUGR or cardiac dysfunction—a poor prognostic sign. EDV is angle-dependent and requires strict attention to measurement technique. EDV is best used in conjunction with PSV and other Doppler parameters to characterize the pattern of flow disturbance and guide clinical management.
Clinical Decision Thresholds (MCA EDV)
EDV patterns and flow classification:
High-output flow pattern (anemia/acute hypoxia):
• Elevated EDV + Elevated PSV + Elevated mean velocity → High-output compensatory state
• Clinical context: Fetal anemia, acute hypoxia, or high-output cardiac state
• Associated findings: Low RI/PI; PSV > 1.5 MoM; may have elevated UA PI (placental insufficiency)
• Management: Confirm anemia with cordocentesis if indicated; plan transfusion or delivery
Low-output flow pattern (IUGR/cardiac dysfunction):
• Reduced EDV + Reduced PSV + Reduced mean velocity → Low-output failure state
• Clinical context: Severe IUGR, cardiac dysfunction, or imminent decompensation
• Associated findings: Elevated RI/PI; elevated UA PI; may have abnormal DV Doppler
• Management: Urgent delivery if ≥32 weeks; assess for cardiac anomalies; prepare for intensive neonatal care
Discordant flow pattern (selective diastolic abnormality):
• Elevated EDV + Normal PSV or Reduced EDV + Normal PSV → Unusual pattern
• Clinical context: Rare; may indicate measurement artifact, specific vascular lesion, or unusual hemodynamic state
• Management: Verify measurement technique; repeat with angle verification; assess for technical error before diagnosing pathology
EDV measurement and interpretation guidelines:
Measurement technique critical points:
• Angle of insonation: Must be as close to 0° as possible; even 10° angle error can result in 15–20% error in EDV value.
• Identify end-diastolic point: Point just before next systolic rise; not the trough of any diastolic notch if present.
• Sample volume placement: Center in vessel lumen; avoid vessel walls or turbulent flow regions.
• Baseline adjustment: Critical for accurate diastolic measurement; misalignment causes systematic errors in low-velocity measurements.
EDV in anemia detection:
• Elevated EDV with elevated PSV (>1.5 MoM): Consistent with anemia; high-output compensatory state
• EDV > 95th centile + PSV normal: Less specific; may represent partial compensation or non-anemic cause
• Serial EDV rising + PSV rising: Progressive anemia; requires intervention planning
• Isolated EDV elevation without PSV elevation: Consider measurement error; verify with repeat scan
EDV in IUGR and placental insufficiency:
• Low EDV with elevated UA PI: Indicates brain-sparing effect inadequate; concerning for IUGR
• Progressive EDV decline + rising UA PI: Indicates deteriorating fetal status; urgent delivery needed
• EDV < 5th centile + low PSV: Indicates severe compromise; poor prognosis
Cerebroplacental hemodynamic patterns using EDV:
• High EDV (>95th) + High UA EDV (>95th): Both high-output state; unusual; evaluate for systemic causes
• High EDV (>95th) + Low UA EDV (<5th): Classic brain-sparing pattern; cerebral vasodilation with placental insufficiency
• Low EDV (<5th) + Low UA EDV (<5th): Universal low-output state; severe compromise; poor prognosis
• Low EDV (<5th) + High UA EDV (>95th): Paradoxical pattern; rare; evaluate for measurement error or unusual pathology
EDV-guided clinical management and decision points:
At ≥34 weeks gestation:
• EDV > 95th centile + PSV > 1.5 MoM + confirmed anemia → Delivery recommended
• EDV < 5th centile + abnormal UA Doppler → Delivery recommended
• EDV progressively declining + UA PI rising → Urgent delivery
At 32–33 weeks gestation:
• EDV > 95th centile + PSV > 1.5 MoM → Cordocentesis for anemia confirmation; prepare for intervention
• EDV < 5th centile + elevated UA PI → Daily CTG; consider delivery if other signs of compromise
• EDV progressively changing (rising or declining) → Intensive surveillance every 3–5 days
Before 32 weeks gestation:
• EDV > 95th centile + PSV > 1.5 MoM in Rh disease → Cordocentesis; consider intrauterine transfusion
• Isolated EDV abnormality without other findings → Serial monitoring every 5–7 days
• Progressive EDV change → More frequent assessments; consider earlier intervention
Key points to remember:
• MCA EDV increases with advancing gestation (normal trend from ~10 cm/s at 20 weeks to ~40 cm/s at 40 weeks).
• EDV is angle-dependent — maintain angle of insonation <0° and be consistent for reproducible measurements.
• Always interpret MCA EDV against gestational-age-specific centiles, not absolute values.
• EDV pattern (elevated vs. reduced) must be interpreted with PSV to determine flow state (high-output vs. low-output).
• Elevated EDV + Elevated PSV = High-output state (anemia or acute hypoxia); indicates compensatory mechanism.
• Reduced EDV + Reduced PSV = Low-output state (IUGR or cardiac dysfunction); indicates failure of compensation.
• Measure on the M1 segment of MCA, proximal to branching, maintaining consistent technique.
• Serial EDV assessment superior to single measurements — trending over time detects progressive changes and guides intervention timing.
• Combine EDV with PSV, RI, PI, and UA Doppler for comprehensive hemodynamic characterization.
• EDV is particularly valuable for distinguishing anemia (high EDV + high PSV) from IUGR (low EDV + low PSV).
• Rapidly rising EDV is concerning — indicates acute worsening of anemia or hypoxia; requires urgent intervention planning.
• Rapidly declining EDV is alarming — indicates acute deterioration in cerebral perfusion; requires immediate assessment and urgent delivery.
• Use EDV in context of complete Doppler profile (MCA RI/PI, PSV, mean velocity, UA Doppler, DV Doppler) for optimal clinical decision-making.
Mean Velocity (MV) → Mean Velocity (MV) is the average blood flow velocity throughout the entire cardiac cycle in the middle cerebral artery. It is calculated as the area under the Doppler waveform envelope divided by the cardiac cycle duration. Unlike ratio-based indices (S/D, RI, PI), mean velocity is an absolute velocity measurement that directly reflects overall blood flow and is highly dependent on angle of insonation. Mean velocity is used in conjunction with PSV and EDV to calculate resistance indices and to assess fetal cerebral perfusion and cardiac output.
Formula:
Mean Velocity (MV) = Area under the velocity-time waveform ÷ Cardiac cycle duration
Approximate MV ≈ (S + 2D) ÷ 3 (simplified estimation)
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. Mean velocity increases with gestational age due to progressive increase in fetal cardiac output and improved cerebral perfusion. Mean velocity reflects the integrated flow throughout the entire cardiac cycle, providing a comprehensive view of cerebral hemodynamics.
In fetal anemia, the reduced oxygen-carrying capacity of blood triggers compensatory cerebral vasodilation and increased cardiac output, resulting in elevated mean velocity. Mean velocity is particularly useful in calculating the Pulsatility Index (PI), which is derived from the formula: PI = (S - D) ÷ MV.
Conversely, in severe IUGR with hypoxia and poor cardiac function, mean velocity may be low or reduced as the fetus attempts to conserve energy and reduce metabolic demands.
As gestation advances from 20 to 40 weeks, the fetal heart becomes more efficient, cardiac output increases, and mean velocity progressively increases. Mean velocity values must be interpreted in the context of gestational age-specific nomograms.
• 20 weeks: ~20–28 cm/s (developing circulation, lower velocities)
• 28 weeks: ~32–45 cm/s (increasing with fetal growth)
• 34 weeks: ~42–55 cm/s
Measuring technique for Mean Velocity:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA.
4. Adjust the angle of insonation as close to 0° as possible — angle correction is critical for mean velocity measurements.
5. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
6. Most ultrasound machines automatically calculate the mean velocity from the velocity-time integral (the area enclosed by the Doppler waveform).
7. Take the mean of 3 measurements for reporting.
8. Always note the angle of insonation used in the report, as small angle variations significantly affect mean velocity values.
9. Mean velocity is essential for calculating PI (Pulsatility Index) and for comprehensive hemodynamic assessment.
Normal Mean Velocity Reference Values for MCA by Gestational Age
Abnormal patterns:
• Mean Velocity > 95th centile for GA → Elevated mean velocity throughout cardiac cycle; indicates increased cardiac output and cerebral blood flow. Reflects high-output compensatory state in response to hypoxia or anemia.
• Mean Velocity < 5th centile for GA → Reduced mean velocity throughout cardiac cycle; indicates decreased cardiac output and cerebral perfusion. Suggests severe IUGR, cardiac dysfunction, or critical fetal compromise.
• Mean Velocity progressively rising on serial scans → Progressive increase in overall cerebral blood flow; indicates worsening anemia or hypoxia with increasing compensatory cardiac output.
• Mean Velocity progressively declining on serial scans → Progressive decrease in overall cerebral blood flow; indicates deteriorating cardiac function and fetal status.
• Elevated Mean Velocity with elevated PSV and EDV → Uniform increase in flow throughout cardiac cycle; consistent with high-output state typical of fetal anemia or acute hypoxia.
• Reduced Mean Velocity with reduced PSV and EDV → Uniform decrease in flow throughout cardiac cycle; consistent with low-output failure associated with severe IUGR or cardiac dysfunction.
Clinical significance and advantages of Mean Velocity:
Unlike ratio-based indices (S/D, RI, PI), mean velocity is an absolute velocity measurement that directly reflects the integrated blood flow throughout the entire cardiac cycle. Mean velocity is essential for calculating Pulsatility Index (PI) and provides a comprehensive view of overall cerebral perfusion independent of waveform morphology. Mean velocity is particularly sensitive for detecting global changes in cardiac output and is useful for distinguishing between hemodynamic states: elevated mean velocity indicates high-output compensation (anemia, hypoxia), while reduced mean velocity indicates low-output failure (severe IUGR, cardiac dysfunction). Mean velocity is angle-dependent and requires strict attention to measurement technique. Mean velocity is best used in conjunction with PSV, EDV, and resistance indices to characterize the complete hemodynamic profile and guide clinical management.
Clinical Decision Thresholds (MCA Mean Velocity)
Mean Velocity patterns and hemodynamic states:
High-output flow pattern (anemia/acute hypoxia):
• Elevated Mean Velocity + Elevated PSV + Elevated EDV + Low RI/PI → High-output compensatory state
• Magnitude: Mean Velocity > 95th centile; PSV > 1.5 MoM; EDV > 95th centile
• PI contribution: PI remains relatively low despite high absolute velocities because the normalized ratio accounts for proportional increase throughout cycle
• Clinical context: Fetal anemia, acute hypoxia, high-output cardiac state
• Associated findings: May have elevated UA PI (placental insufficiency); normal or elevated mean velocity in umbilical artery
• Management: Confirm anemia with cordocentesis if indicated; plan transfusion or delivery; serial mean velocity trending guides timing of intervention
Low-output flow pattern (IUGR/cardiac dysfunction):
• Reduced Mean Velocity + Reduced PSV + Reduced EDV + High RI/PI → Low-output failure state
• Magnitude: Mean Velocity < 5th centile; PSV < 5th centile; EDV < 5th centile
• PI contribution: PI may be normal or even relatively low despite low absolute velocities because the normalized ratio is preserved
• Clinical context: Severe IUGR, cardiac dysfunction, imminent decompensation
• Associated findings: Elevated UA PI; abnormal DV Doppler (reversed flow, absent flow); may have cardiac anomalies on ultrasound
• Management: Urgent delivery if ≥32 weeks; assess for cardiac anomalies; prepare for intensive neonatal care; poor prognosis
Preserved mean velocity with abnormal PI/RI (unusual pattern):
• Normal Mean Velocity + Elevated RI/PI + Low EDV → High resistance despite maintained mean flow
• Mechanism: Reduced diastolic flow offset by increased systolic flow; results in relatively preserved mean but abnormal resistance indices
• Clinical interpretation: Early or developing resistance increase; possible transition state between compensation and decompensation
• Management: Serial monitoring; assess for progression to true low-output state
Elevated mean velocity with elevated resistance indices (paradoxical pattern):
• Elevated Mean Velocity + Elevated RI/PI → Unusual combination; suggests specific pathology
• Possible causes: Measurement error, unusual waveform morphology, specific vascular lesions
• Management: Verify measurement technique with angle verification; repeat if questionable; assess for technical error before diagnosing pathology
Mean Velocity measurement and interpretation guidelines:
Measurement technique critical points:
• Angle of insonation: Must be as close to 0° as possible; angle error affects both PSV and EDV equally, but mean velocity calculation requires accurate envelope integration.
• Velocity-time integral (VTI): Mean velocity calculated from area under the Doppler waveform envelope divided by cardiac cycle duration.
• Waveform quality: Clear, well-defined envelope essential for accurate mean velocity calculation; poor signal degrades mean velocity accuracy.
• Sample volume placement: Center in vessel lumen; avoid vessel walls or turbulent flow regions that distort waveform.
• Baseline adjustment: Critical for accurate integration; misalignment affects mean velocity calculation significantly.
Mean velocity in cardiac output assessment:
• Mean velocity > 95th centile: Indicates increased cardiac output; consistent with fetal compensation to anemia or hypoxia
• Mean velocity < 5th centile: Indicates reduced cardiac output; concerning for cardiac dysfunction or severe compromise
• Serial mean velocity rising: Progressive increase in cardiac output; indicates worsening anemia or compensatory response
• Serial mean velocity declining: Progressive decrease in cardiac output; indicates deteriorating fetal status
Mean velocity in anemia detection:
• Elevated Mean Velocity + PSV > 1.5 MoM + Elevated EDV: Consistent with anemia; high-output compensatory state
• Mean Velocity borderline + PSV borderline: May represent mild anemia or early compensation; requires clinical correlation
• Serial mean velocity trending with PSV: Parallel changes suggest uniform high-output state; divergent changes suggest measurement error or unusual pattern
Mean velocity in IUGR and placental insufficiency:
• Low Mean Velocity with elevated UA PI: Indicates inadequate brain-sparing effect; concerning for severe IUGR
• Progressive Mean Velocity decline + rising UA PI: Indicates deteriorating fetal status and cardiac decompensation; urgent delivery needed
• Mean Velocity < 5th centile + PSV normal: Unusual pattern; suggests selective reduction in flow averaging; evaluate for technical error
Mean Velocity and PI relationship:
• PI = (PSV - EDV) ÷ Mean Velocity
• Elevated Mean Velocity with low RI/PI: Indicates high-output state with appropriate vasodilation
• Reduced Mean Velocity with high RI/PI: Indicates low-output state with high resistance
• Mean Velocity critical for PI calculation: Errors in mean velocity measurement directly affect PI accuracy
Mean Velocity-guided clinical management and decision points:
At ≥34 weeks gestation:
• Mean Velocity > 95th centile + PSV > 1.5 MoM + confirmed anemia → Delivery recommended
• Mean Velocity < 5th centile + abnormal UA Doppler → Delivery recommended
• Mean Velocity progressively declining + UA PI rising → Urgent delivery
• Rapid Mean Velocity change → Immediate delivery consideration
At 32–33 weeks gestation:
• Mean Velocity > 95th centile + PSV > 1.5 MoM → Cordocentesis for anemia confirmation; prepare for intervention
• Mean Velocity < 5th centile + elevated UA PI → Daily CTG; consider delivery if other signs of compromise present
• Mean Velocity progressively changing (rising or declining) → Intensive surveillance every 3–5 days; prepare for intervention
Before 32 weeks gestation:
• Mean Velocity > 95th centile + PSV > 1.5 MoM in Rh disease → Cordocentesis; consider intrauterine transfusion
• Isolated Mean Velocity abnormality without other findings → Serial monitoring every 5–7 days
• Progressive Mean Velocity change → More frequent assessments; consider earlier intervention
Cerebroplacental hemodynamic patterns using Mean Velocity:
• High MCA Mean Velocity + Normal UA Mean Velocity: Cerebral high-output state; suggests brain-sparing effect
• High MCA Mean Velocity + High UA Mean Velocity: Global high-output state; suggests systemic compensation (severe anemia, hypoxia)
• Low MCA Mean Velocity + Low UA Mean Velocity: Global low-output state; severe compromise; poor prognosis
• Low MCA Mean Velocity + Normal UA Mean Velocity: Selective cerebral reduction; suggests primary cerebral compromise or cardiac dysfunction
Key points to remember:
• MCA Mean Velocity increases
Diastolic Notch → Diastolic Notch is a brief reversal or deceleration of blood flow velocity during mid-to-late diastole in the middle cerebral artery waveform. It appears as a characteristic dip or indentation in the descending limb of the Doppler waveform, typically occurring in early gestation and progressively disappearing as pregnancy advances. The presence or absence of a diastolic notch can provide qualitative information about cerebral vascular resistance, vascular maturation, and fetal hemodynamic status.
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. A diastolic notch represents transient flow deceleration caused by the compliance mismatch between the proximal cerebral vessels and the distal vascular bed during early gestation. The notch reflects high vascular resistance in the distal cerebral circulation.
As gestation advances and the cerebral vascular bed matures through progressive vasodilation and angiogenesis, the vascular compliance improves, resistance decreases, and the diastolic notch progressively smooths out and disappears.
In IUGR with placental insufficiency and fetal hypoxia, the normal progression of notch disappearance may be delayed or the notch may persist abnormally, suggesting inadequate cerebral vascular maturation or persistent high resistance. However, the presence of a diastolic notch in early gestation is NORMAL and expected.
Conversely, in fetal anemia, the cerebral vasculature undergoes vasodilation and the notch may disappear prematurely or be absent from the outset, reflecting low resistance and increased diastolic flow.
• Early gestation (20–24 weeks): Diastolic notch PRESENT (normal finding)
• Mid-gestation (26–30 weeks): Notch progressively disappearing
• Late gestation (32+ weeks): Notch typically ABSENT (smooth diastolic flow)
Measuring technique for Diastolic Notch assessment:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA with angle of insonation close to 0°.
4. Measure during fetal rest (no breathing / movement), capture at least 2–3 clear waveforms.
5. Examine the descending limb (diastolic portion) of the waveform carefully for any visible dip, notch, or reversal pattern.
6. Note whether a notch is present, absent, or borderline.
7. If present, assess the depth and timing of the notch in relation to the cardiac cycle.
8. Always correlate with gestational age — notch presence must be interpreted in context of normal gestation-dependent progression.
9. Serial assessment can help track vascular maturation and detect abnormal patterns.
Diastolic Notch Presence by Gestational Age
Abnormal patterns:
• Notch persisting beyond 32 weeks → Delayed disappearance of diastolic notch; indicates inadequate cerebral vascular maturation or resistance abnormality. May suggest IUGR, growth restriction, or placental insufficiency.
• Notch abnormally prominent or deep → Exaggerated flow deceleration in mid-to-late diastole; may indicate transient hemodynamic disturbances or specific vascular abnormalities.
• Notch absent prematurely (before 20 weeks) → Early disappearance of diastolic notch; unusual finding; may indicate abnormal cerebral vascular development or measurement artifact.
• Notch re-appearing on serial scans → Reappearance of previously absent notch in late gestation; rare finding; may indicate acute hemodynamic changes or vascular disturbance.
• Abnormal notch morphology → Notch with unusual shape, timing, or depth; may indicate specific flow patterns or vascular lesions.
• Notch present with elevated RI/PI/S/D → Persistent notch associated with high cerebral vascular resistance; indicates delayed vascular maturation and inadequate cerebral compensation.
• Notch present with low RI/PI/S/D → Unusual combination; notch present despite low resistance; may indicate unique hemodynamic state or measurement artifact.
Clinical significance of diastolic notch patterns:
The diastolic notch is a qualitative morphological feature of the MCA Doppler waveform that reflects vascular compliance and resistance maturation. Normal notch progression (present early, progressively smoothing, absent by 32 weeks) is reassuring and indicates normal cerebral vascular development. Abnormal notch patterns (persistence, delayed disappearance, re-appearance) may indicate delayed cerebral vascular maturation, IUGR, or placental insufficiency. The notch is best interpreted in conjunction with quantitative Doppler indices (RI, PI, S/D) and clinical context. Abnormal notch patterns warrant further evaluation with growth parameters, UA Doppler, and serial monitoring. The diastolic notch is more of a supportive qualitative finding than a primary diagnostic parameter; quantitative indices (RI, PI) are generally more reliable for clinical decision-making.
Clinical Decision Thresholds (MCA Diastolic Notch)
Notch patterns and their clinical correlations:
Normal progressive notch pattern (reassuring):
• Pattern: Notch present at 20–26 weeks; progressively becomes shallower and smoother; absent by 32–34 weeks
• Associated findings: RI/PI/S/D values progressively decreasing with GA; PSV/EDV progressively increasing; normal growth trajectory
• Clinical significance: Normal cerebral vascular maturation; reflects expected progression of vascular development and decreasing resistance
• Management: Routine surveillance; reassuring finding; no intervention indicated
Delayed notch disappearance (abnormal pattern):
• Pattern: Notch still present at 32+ weeks when it should be absent; persistent beyond normal timeline
• Associated findings: RI/PI/S/D values elevated or not decreasing appropriately; may have growth restriction on biometry; may have elevated UA PI
• Clinical significance: Delayed cerebral vascular maturation; suggests inadequate vascular development or IUGR; indicates resistance not decreasing normally
• Management: Evaluate biometry for growth restriction; assess all Doppler parameters (RI, PI, S/D, UA Doppler); serial monitoring every 1–2 weeks; consider delivery if ≥34 weeks with confirmed growth restriction
Persistent notch with elevated RI/PI (concerning pattern):
• Pattern: Notch present beyond 32 weeks AND elevated RI/PI/S/D for GA
• Associated findings: Growth restriction common; elevated UA PI suggesting placental insufficiency; low PSV/EDV relative to GA
• Clinical significance: Combined evidence of delayed maturation and high resistance; indicates significant cerebral vascular compromise and inadequate fetal compensation
• Management: URGENT evaluation; strongly consider delivery if ≥34 weeks; prepare for possible early delivery; assess for IUGR-related complications
Persistent notch with low RI/PI (unusual pattern):
• Pattern: Notch present beyond 32 weeks BUT RI/PI/S/D values are low (opposite of expected)
• Possible explanation: Rare pattern; may indicate unusual hemodynamic state with selective diastolic disturbance; possible measurement artifact
• Clinical significance: Unclear; may represent transient flow phenomenon or specific vascular characteristic
• Management: Verify measurement technique; repeat assessment with careful angle verification; correlate with PSV/EDV; assess for technical error
Abnormally prominent/exaggerated notch:
• Pattern: Notch depth unusually marked; significant diastolic flow reversal or deceleration at any GA
• Associated findings: May have abnormal RI/PI; may have cardiac abnormalities; may have vascular lesions
• Clinical significance: May indicate transient hemodynamic disturbance, specific vascular abnormality, or measurement artifact
• Management: Correlate with quantitative indices; detailed fetal cardiac and cerebral ultrasound; serial assessment; investigate for underlying pathology
Early notch disappearance (notch absent before 20 weeks):
• Pattern: Diastolic notch not visible at 16–20 weeks when presence is expected
• Associated findings: Unusually low RI/PI for GA; elevated PSV/EDV; may have fetal anemia or other systemic condition
• Clinical significance: Unusual; suggests either early cerebral vasodilation or abnormal vascular development; requires investigation
• Management: Assess for fetal anemia (check PSV for MoM); detailed fetal ultrasound for anomalies; investigate for hemolytic disease or other pathology; serial assessment
Notch assessment technique and interpretation guidelines:
Optimal notch visualization:
• Waveform quality: Clear, well-defined Doppler envelope essential; poor signal obscures notch detection
• Sample placement: Proximal M1 segment provides best notch visualization; distal MCA may have less prominent notch
• Multiple waveforms: Assess at least 2–3 cardiac cycles; notch may vary slightly cycle-to-cycle
• Fetal state: Notch assessment during fetal rest (no breathing/movement) most reliable
Notch identification and documentation:
• Visual assessment: Identify dip or indentation in descending (diastolic) limb of waveform
• Timing: Notch occurs in mid-to-late diastole; just before end-diastolic point
• Depth: Record depth and prominence (shallow vs. deep/exaggerated)
• Documentation: Report as "present," "absent," "borderline," or "prominent/exaggerated"
• Serial notation: Compare with prior scans to assess progression pattern
Distinguishing notch from other waveform features:
• Diastolic notch: Transient reversal/deceleration in mid-to-late diastole; normal in early gestation
• End-diastolic flow reversal: Complete reversal (negative velocity) at end-diastole; abnormal even in early gestation; indicates severe resistance
• Diastolic oscillations: Multiple undulations in diastole; different from simple notch; may indicate turbulent flow
• Spectral broadening: Widened velocity envelope; different finding; indicates turbulence
Notch-guided clinical management and decision points:
At ≥36 weeks gestation:
• Notch still present → Delivery should be strongly considered, especially if ≥37 weeks
• Notch present + elevated RI/PI → Urgent delivery recommendation
• Notch present + growth restriction → Delivery recommended
At 32–35 weeks gestation:
• Notch persisting + normal RI/PI + normal growth → Serial Doppler every 1–2 weeks; deliver at 37+ weeks
• Notch persisting + elevated RI/PI → Consider delivery if other signs of compromise present
• Notch persisting + growth restriction + abnormal UA Doppler → Delivery consideration at 34+ weeks
Before 32 weeks gestation:
• Notch present (normal finding) + normal RI/PI + normal growth → Routine surveillance
• Notch persisting (abnormal for GA) → Serial Doppler assessment; prepare for possible early delivery decision
Serial notch assessment and prognostic significance:
• Notch progressively disappearing: Reassuring; normal vascular maturation; no intervention needed
• Notch static (not changing): Concerning; suggests failed normal maturation; warrants investigation
• Notch becoming more prominent: Unusual; may indicate deteriorating hemodynamics; requires urgent assessment
• Notch re-appearing after disappearance: Rare and concerning; suggests acute hemodynamic change; requires urgent evaluation
Key points to remember:
• Diastolic notch normal at 20–26 weeks; reflects high cerebral vascular resistance and developing circulation.
• Progressive notch smoothing 26–32 weeks is expected and indicates normal vascular maturation.
• Notch should be absent by 32–34 weeks in normal pregnancy.
• Notch persisting beyond 32 weeks is abnormal and suggests delayed vascular maturation or IUGR.
• Diastolic notch is a qualitative supportive finding; quantitative indices (RI, PI, S/D) are primary parameters for clinical decision-making.
• Correlate notch findings with quantitative Doppler indices — persistent notch should have elevated RI/PI for interpretation to be consistent.
• Notch presence alone is less predictive than combined assessment (notch + RI/PI + growth parameters + UA Doppler).
• Serial notch assessment more important than isolated finding — trend of progression/disappearance guides management decisions.
• Notch assessment should be part of comprehensive Doppler evaluation; integrate with S/D, RI, PI, PSV, EDV, mean velocity.
• Abnormal notch patterns warrant further investigation for IUGR, growth restriction, or other fetal compromise.
• Notch persisting at term ≥37 weeks + growth restriction or other abnormalities → Delivery recommended.
• Use notch as supportive evidence in context of complete clinical picture, not as sole indicator for intervention.
S/D ratio → S/D ratio (Systolic/Diastolic ratio) is the ratio of peak systolic velocity (S) to end-diastolic velocity (D) in the middle cerebral artery waveform. It is one of the most commonly used Doppler indices to assess cerebral perfusion and detect fetal compromise.
Formula:
S/D ratio = Peak Systolic Velocity (S) ÷ End-Diastolic Velocity (D)
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. Under normal conditions, the brain receives a relatively high-resistance blood supply proportional to body oxygenation. When the fetus becomes hypoxic or anemic, the cerebral vasculature undergoes vasodilation to increase cerebral perfusion—the diastolic flow increases sharply, and the S/D ratio decreases. Conversely, normal or elevated resistance indicates adequate fetal oxygenation.
As gestation advances from 20 to 40 weeks, the cerebral circulation matures, vascular resistance gradually falls, diastolic flow increases, and the S/D ratio progressively decreases.
• 20 weeks: ~4.5–5.0 (high resistance, developing circulation)
• 28 weeks: ~3.5–4.0 (resistance falling)
• 34 weeks: ~2.8–3.2
Measuring technique for S/D:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA with angle of insonation close to 0°.
4. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
5. On each waveform, mark the peak systolic point (S) and the end-diastolic point (D).
6. Most ultrasound machines auto-calculate the S/D ratio; take the mean of 3 waveforms for reporting.
7. Angle correction is not required for ratio-based indices (S/D, RI, PI), as both numerator and denominator are equally affected by the angle.
Normal S/D Ratio Reference Values for MCA by Gestational Age
| GA (weeks) | S/D Ratio (5th–95th centile) | Interpretation |
|---|---|---|
| 20 | 4.5–5.5 | High resistance; developing cerebral circulation |
| 22 | 4.2–5.1 | Resistance gradually falling |
| 24 | 3.9–4.7 | Progressive maturation |
| 26 | 3.7–4.4 | Diastolic flow increasing |
| 28 | 3.5–4.1 | Resistance continuing to fall |
| 30 | 3.3–3.9 | Steady decline in resistance |
| 32 | 3.1–3.7 | Cerebral circulation maturing |
| 34 | 2.9–3.5 | — |
| 36 | 2.7–3.2 | — |
| 38 | 2.5–3.0 | — |
| 40 | 2.3–2.8 | Mature cerebral circulation at term |
| 41–42 | 2.2–2.7 | Stable post-term values |
Abnormal patterns:
• S/D < 5th centile for GA → Reduced cerebral vascular resistance; increased diastolic flow. Indicates cerebral vasodilation in response to hypoxia or anemia. Brain-sparing effect.
• S/D > 95th centile for GA → Elevated cerebral vascular resistance; decreased diastolic flow. Indicates inadequate cerebral vascular maturation or primary cerebral compromise.
• Persistently elevated S/D beyond expected GA → Delayed cerebral vascular maturation; may indicate IUGR, fetal growth restriction, or placental insufficiency with inadequate fetal adaptation.
• Rapidly declining S/D across serial scans → Progressive cerebral vasodilation; suggests worsening fetal hypoxia or development of anemia.
Limitation of S/D ratio:
The S/D ratio is a simple but crude measure of cerebral vascular resistance. It is angle-dependent and becomes unreliable when end-diastolic flow is very low or nearly absent. In situations requiring more precise hemodynamic assessment, the Pulsatility Index (PI) and Resistance Index (RI) are preferred, as they normalize the measurement and are less susceptible to angle variations and flow characteristics. PI and RI remain mathematically valid across the full range of resistance states.
Clinical Decision Thresholds (MCA S/D Ratio)
| MCA S/D Ratio Finding | Cerebral Vascular Resistance | Clinical Interpretation | Clinical Action |
|---|---|---|---|
| Within normal range for GA | Normal | Adequate cerebral perfusion | Routine surveillance |
| > 95th centile for GA | Elevated | High cerebral resistance; inadequate vasodilation | Evaluate for IUGR, growth restriction; serial Doppler every 1–2 weeks |
| < 5th centile for GA | Severely reduced | Cerebral vasodilation; brain-sparing effect | Urgent evaluation for fetal anemia, hypoxia; check PSV/EDV; consider delivery planning if ≥34 weeks |
| Progressively declining S/D | Worsening vasodilation | Progressive fetal compromise | Daily CTG; assess UA Doppler; urgent delivery consideration |
| Persistently elevated S/D beyond 32 weeks | Resistance not decreasing | Delayed maturation; possible IUGR | Assess growth parameters, UA Doppler; consider delivery if other signs of compromise |
Key points to remember:
• MCA S/D ratio decreases with advancing gestation (normal trend from ~4.5 at 20 weeks to ~2.3 at 40 weeks).
• A rising or static MCA S/D ratio across serial scans is concerning even if still within "normal" range — suggests failing compensatory mechanism.
• Always interpret MCA S/D ratio against gestational-age-specific centiles, not a single cut-off value.
• Low MCA S/D ratio (brain-sparing effect) should be correlated with elevated UA S/D ratio (placental insufficiency) for complete picture.
• MCA S/D ratio is angle-dependent — maintain consistent angle of insonation (close to 0°) for reproducible measurements.
• Measure on the M1 segment of MCA, proximal to branching, to avoid measurement artifacts and ensure consistency.
• MCA S/D, RI, and PI are correlated; most centres now report PI as the primary parameter, with S/D as supportive.
• Combine MCA and UA Doppler assessment for comprehensive evaluation: elevated UA resistance + reduced MCA resistance = severe placental insufficiency with brain-sparing effect.
RI (Resistance Index) → RI (Resistance Index) is a normalized Doppler index that reflects vascular resistance in the middle cerebral artery. It is calculated from peak systolic velocity (S) and end-diastolic velocity (D), and is independent of angle of insonation, making it highly reproducible and reliable.
Formula:
RI = (Peak Systolic Velocity - End-Diastolic Velocity) ÷ Peak Systolic Velocity
RI = (S - D) ÷ S
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. Under normal conditions, the brain receives a relatively high-resistance blood supply proportional to body oxygenation. When the fetus becomes hypoxic or anemic, the cerebral vasculature undergoes vasodilation to increase cerebral perfusion—the diastolic flow increases sharply, and the RI decreases. Conversely, normal or elevated resistance indicates adequate fetal oxygenation.
As gestation advances from 20 to 40 weeks, the cerebral circulation matures, vascular resistance gradually falls, diastolic flow increases, and the RI progressively decreases.
• 20 weeks: ~0.82–0.88 (high resistance, developing circulation)
• 28 weeks: ~0.70–0.78 (resistance falling)
• 34 weeks: ~0.62–0.70
Measuring technique for RI:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA with angle of insonation close to 0°.
4. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
5. On each waveform, mark the peak systolic point (S) and the end-diastolic point (D).
6. Most ultrasound machines auto-calculate the RI; take the mean of 3 waveforms for reporting.
7. RI is angle-independent and provides more reliable assessment across different insonation angles compared to S/D ratio.
Normal RI Reference Values for MCA by Gestational Age
| GA (weeks) | RI (5th–95th centile) | Interpretation |
|---|---|---|
| 20 | 0.82–0.90 | High resistance; developing cerebral circulation |
| 22 | 0.80–0.88 | Resistance gradually falling |
| 24 | 0.78–0.85 | Progressive maturation |
| 26 | 0.76–0.83 | Diastolic flow increasing |
| 28 | 0.74–0.80 | Resistance continuing to fall |
| 30 | 0.72–0.78 | Steady decline in resistance |
| 32 | 0.70–0.76 | Cerebral circulation maturing |
| 34 | 0.68–0.74 | — |
| 36 | 0.66–0.72 | — |
| 38 | 0.64–0.70 | — |
| 40 | 0.62–0.68 | Mature cerebral circulation at term |
| 41–42 | 0.60–0.66 | Stable post-term values |
Abnormal patterns:
• RI < 5th centile for GA → Reduced cerebral vascular resistance; increased diastolic flow. Indicates cerebral vasodilation in response to hypoxia or anemia. Brain-sparing effect.
• RI > 95th centile for GA → Elevated cerebral vascular resistance; decreased diastolic flow. Indicates inadequate cerebral vascular maturation or primary cerebral compromise.
• Persistently elevated RI beyond expected GA → Delayed cerebral vascular maturation; may indicate IUGR, fetal growth restriction, or placental insufficiency with inadequate fetal adaptation.
• Rapidly declining RI across serial scans → Progressive cerebral vasodilation; suggests worsening fetal hypoxia or development of anemia.
• Rising or static RI on serial scans → Increasing cerebral resistance; indicates deteriorating fetal status or failed compensatory mechanism.
Advantages of RI over S/D ratio:
The RI is a normalized index that is independent of angle of insonation, making it more reproducible and reliable than S/D ratio across different measurement angles. RI normalizes the relationship between systolic and diastolic velocities and remains mathematically valid even when end-diastolic flow is very low (approaching zero), whereas S/D ratio becomes extremely large or undefined. RI is therefore superior for detecting subtle changes in cerebral resistance and for tracking serial changes over time.
Clinical Decision Thresholds (MCA RI)
| MCA RI Finding | Cerebral Vascular Resistance | Clinical Interpretation | Clinical Action |
|---|---|---|---|
| Within normal range for GA | Normal | Adequate cerebral perfusion; normal vascular maturation | Routine surveillance |
| > 95th centile for GA | Elevated | High cerebral resistance; inadequate vasodilation; delayed maturation | Evaluate for IUGR, growth restriction; assess UA Doppler; serial Doppler every 1–2 weeks |
| < 5th centile for GA | Severely reduced | Cerebral vasodilation; brain-sparing effect; compensatory mechanism | Urgent evaluation for fetal anemia, hypoxia; check PSV/EDV/mean velocity; assess UA Doppler for placental insufficiency |
| RI < 0.55 at term (≥38 weeks) | Critically reduced | Severe cerebral vasodilation; marked brain-sparing effect | Immediate fetal assessment; consider delivery if ≥34 weeks with other signs of compromise |
| Progressively declining RI | Worsening vasodilation | Progressive fetal compensation or decompensation | Daily CTG; assess all Doppler parameters (UA, MCA, DV); urgent delivery consideration |
| Rising RI on serial scans | Increasing resistance | Deteriorating cerebral perfusion; failed compensation | Daily CTG; assess growth; prepare for urgent delivery if ≥32 weeks |
| RI > 0.85 at term (≥38 weeks) | Persistently elevated | Abnormal resistance pattern at term; suggests compromise | Assess fetal biometry, UA/MCA/DV Doppler pattern; strongly consider delivery |
RI value patterns and their clinical significance:
Cerebroplacental Ratio (CPR): CPR = MCA RI ÷ UA RI
• Normal CPR (≥ 1.0 at term): MCA resistance lower than or equal to UA resistance; normal placental-cerebral relationship
• Abnormal CPR (< 1.0 at term): MCA resistance higher than UA resistance; indicates failed brain-sparing effect; associated with worse outcomes
• Markedly reduced MCA RI with elevated UA RI: Severe placental insufficiency with appropriate brain-sparing compensation; imminent fetal decompensation risk
Serial RI assessment:
• Stable RI within normal range: Reassuring; continue routine surveillance
• RI declining (improving): Normal vascular maturation; favorable sign
• RI static or rising: Concerning pattern; suggests failure of normal maturation or progressive compromise
• Rapid changes in RI: Indicates acute hemodynamic shifts; requires urgent evaluation and intervention planning
Key points to remember:
• MCA RI decreases with advancing gestation (normal trend from ~0.85 at 20 weeks to ~0.65 at 40 weeks).
• A rising or static MCA RI across serial scans is concerning and indicates abnormal resistance progression.
• Always interpret MCA RI against gestational-age-specific centiles, not a single cut-off value.
• Low MCA RI (brain-sparing effect) should be correlated with elevated UA RI (placental insufficiency) for complete assessment.
• MCA RI is angle-independent — more reproducible than S/D ratio; allows reliable serial comparisons even with slight angle variations.
• Measure on the M1 segment of MCA, proximal to branching, to ensure consistent measurements.
• Combine MCA and UA RI assessment — calculate Cerebroplacental Ratio (CPR) for comprehensive evaluation of fetal hemodynamic status.
• CPR < 1.0 at term is abnormal and indicates failure of brain-sparing compensation; associated with increased perinatal mortality.
• MCA RI, S/D, and PI are correlated; RI provides normalized, angle-independent assessment superior to S/D for detecting subtle changes.
• Consider umbilical artery (UA) RI, middle cerebral artery (MCA) RI, and cerebroplacental ratio (CPR) as the foundation of Doppler assessment in high-risk pregnancies.
PI (Pulsatility Index) → PI (Pulsatility Index) is a normalized Doppler index that reflects vascular resistance and compliance in the middle cerebral artery. It is calculated from peak systolic velocity (S), end-diastolic velocity (D), and mean velocity (M), and is independent of angle of insonation, making it highly reproducible and reliable for assessing fetal cerebral perfusion.
Formula:
PI = (Peak Systolic Velocity - End-Diastolic Velocity) ÷ Mean Velocity
PI = (S - D) ÷ M
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. Under normal conditions, the brain receives a relatively high-resistance blood supply proportional to body oxygenation. When the fetus becomes hypoxic or anemic, the cerebral vasculature undergoes vasodilation to increase cerebral perfusion—the diastolic flow increases sharply, and the PI decreases. Conversely, normal or elevated resistance indicates adequate fetal oxygenation.
As gestation advances from 20 to 40 weeks, the cerebral circulation matures, vascular resistance gradually falls, diastolic flow increases, and the PI progressively decreases. PI is considered more sensitive than RI and S/D ratio for detecting subtle changes in cerebral hemodynamics.
• 20 weeks: ~2.0–2.3 (high resistance, developing circulation)
• 28 weeks: ~1.5–1.8 (resistance falling)
• 34 weeks: ~1.2–1.5
Measuring technique for PI:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA with angle of insonation close to 0°.
4. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
5. On each waveform, identify the peak systolic point (S), end-diastolic point (D), and calculate or identify the mean velocity (M).
6. Most ultrasound machines auto-calculate the PI; take the mean of 3 waveforms for reporting.
7. PI is angle-independent and provides superior assessment of vascular resistance and compliance compared to S/D ratio and RI.
Normal PI Reference Values for MCA by Gestational Age
| GA (weeks) | PI (5th–95th centile) | Interpretation |
|---|---|---|
| 20 | 2.0–2.4 | High resistance; developing cerebral circulation |
| 22 | 1.9–2.3 | Resistance gradually falling |
| 24 | 1.8–2.1 | Progressive maturation |
| 26 | 1.7–2.0 | Diastolic flow increasing |
| 28 | 1.6–1.9 | Resistance continuing to fall |
| 30 | 1.5–1.8 | Steady decline in resistance |
| 32 | 1.4–1.7 | Cerebral circulation maturing |
| 34 | 1.3–1.6 | — |
| 36 | 1.2–1.5 | — |
| 38 | 1.1–1.4 | — |
| 40 | 1.0–1.3 | Mature cerebral circulation at term |
| 41–42 | 0.95–1.2 | Stable post-term values |
Abnormal patterns:
• PI < 5th centile for GA → Reduced cerebral vascular resistance; increased diastolic flow. Indicates cerebral vasodilation in response to hypoxia or anemia. Brain-sparing effect.
• PI > 95th centile for GA → Elevated cerebral vascular resistance; decreased diastolic flow. Indicates inadequate cerebral vascular maturation or primary cerebral compromise.
• Persistently elevated PI beyond expected GA → Delayed cerebral vascular maturation; may indicate IUGR, fetal growth restriction, or placental insufficiency with inadequate fetal adaptation.
• Rapidly declining PI across serial scans → Progressive cerebral vasodilation; suggests worsening fetal hypoxia or development of anemia.
• Rising or static PI on serial scans → Increasing cerebral resistance; indicates deteriorating fetal status or failed compensatory mechanism.
Advantages of PI over S/D ratio and RI:
The PI is considered the gold standard Doppler index for cerebral vascular resistance assessment because it is completely independent of angle of insonation and incorporates mean velocity in its calculation. PI is the most sensitive for detecting subtle hemodynamic changes and provides superior discrimination between normal and abnormal resistance states. Unlike S/D ratio, PI remains mathematically valid even when end-diastolic flow is extremely low or nearly absent. PI is more robust for serial comparisons and is the preferred primary parameter in most fetal medicine centres for comprehensive hemodynamic evaluation.
Clinical Decision Thresholds (MCA PI)
| MCA PI Finding | Cerebral Vascular Resistance | Clinical Interpretation | Clinical Action |
|---|---|---|---|
| Within normal range for GA | Normal | Adequate cerebral perfusion; normal vascular maturation | Routine surveillance |
| > 95th centile for GA | Elevated | High cerebral resistance; inadequate vasodilation; delayed maturation | Evaluate for IUGR, growth restriction; assess UA Doppler; serial Doppler every 1–2 weeks |
| < 5th centile for GA | Severely reduced | Cerebral vasodilation; brain-sparing effect; compensatory mechanism | Urgent evaluation for fetal anemia, hypoxia; check PSV/EDV/mean velocity; assess UA Doppler for placental insufficiency |
| PI < 1.0 at term (≥38 weeks) | Critically reduced | Severe cerebral vasodilation; marked brain-sparing effect | Immediate fetal assessment; daily CTG; consider delivery if ≥34 weeks with other signs of compromise |
| Progressively declining PI | Worsening vasodilation | Progressive fetal compensation or decompensation; increasing anemia or hypoxia | Daily CTG; assess all Doppler parameters (UA, MCA, DV); check hematocrit if anemia suspected; urgent delivery consideration |
| Rising PI on serial scans | Increasing resistance | Deteriorating cerebral perfusion; failed compensation; worsening IUGR | Daily CTG; assess growth parameters; assess UA/DV Doppler; prepare for urgent delivery if ≥32 weeks |
| PI > 1.5 at term (≥38 weeks) | Persistently elevated | Abnormal resistance pattern at term; suggests inadequate maturation or primary compromise | Assess fetal biometry, UA/MCA/DV Doppler pattern; strongly consider delivery; investigate for underlying fetal anomalies |
PI value patterns and their clinical significance:
Cerebroplacental Ratio using PI (PI-CPR): PI-CPR = MCA PI ÷ UA PI
• Normal PI-CPR (≥ 1.0 at term): MCA resistance lower than or equal to UA resistance; normal placental-cerebral relationship; appropriate brain perfusion
• Abnormal PI-CPR (< 1.0 at term): MCA resistance higher than UA resistance; indicates failed brain-sparing effect; associated with worse perinatal outcomes
• Markedly reduced MCA PI with elevated UA PI: Severe placental insufficiency with appropriate brain-sparing compensation; indicates significant fetal compromise
• PI-CPR < 0.9 at term: High risk for adverse outcome; consider delivery planning
Serial PI assessment and trend analysis:
• Stable PI within normal range: Reassuring; continue routine surveillance
• PI declining (improving): Normal vascular maturation; favorable sign; expected pattern
• PI static or rising: Concerning pattern; suggests failure of normal maturation or progressive compromise
• Rapid changes in PI (>0.2 unit change): Indicates acute hemodynamic shifts; requires urgent evaluation and immediate intervention planning
• Crossing centile lines downward: Reassuring progression; normal maturation
• Crossing centile lines upward: Concerning; indicates abnormal resistance increase; requires urgent assessment
PI-guided clinical management thresholds:
At ≥34 weeks gestation:
• MCA PI > 95th centile + abnormal UA Doppler → Consider delivery
• MCA PI < 5th centile + elevated UA PI → Consider delivery
• PI-CPR < 1.0 + other concerning features → Delivery recommended
At 32–33 weeks gestation:
• MCA PI < 5th centile + UA RI > 95th centile → Daily CTG; consider delivery if other signs of compromise present
• Progressive worsening of PI on serial scans → Intensive surveillance; prepare for emergency delivery
Key points to remember:
• MCA PI decreases with advancing gestation (normal trend from ~2.0 at 20 weeks to ~1.0 at 40 weeks).
• A rising or static MCA PI across serial scans is concerning and indicates abnormal resistance progression.
• Always interpret MCA PI against gestational-age-specific centiles, not a single cut-off value.
• Low MCA PI (brain-sparing effect) should be correlated with elevated UA PI (placental insufficiency) for complete assessment.
• MCA PI is the most angle-independent and reproducible of all Doppler indices; ideal for serial comparisons over time.
• Measure on the M1 segment of MCA, proximal to branching, to ensure consistent measurements.
• Calculate Cerebroplacental Ratio using PI (PI-CPR = MCA PI ÷ UA PI) for comprehensive evaluation of fetal hemodynamic status.
• PI-CPR < 1.0 at term is abnormal and indicates failure of brain-sparing compensation; associated with increased perinatal morbidity and mortality.
• Trending PI values is more important than absolute values — serial assessment detects progressive changes earlier than isolated measurements.
• MCA PI is the preferred primary Doppler parameter in fetal medicine; S/D and RI are supportive.
• Use MCA PI, UA PI, and PI-CPR as the foundation of Doppler assessment in high-risk pregnancies; supplement with DV Doppler when severe compromise suspected.
PSV (Peak Systolic Velocity) → PSV (Peak Systolic Velocity) is the maximum blood flow velocity during ventricular systole in the middle cerebral artery. Unlike ratio-based indices (S/D, RI, PI), PSV is an absolute velocity measurement that directly reflects blood flow speed and is highly dependent on angle of insonation. PSV is increasingly used to assess fetal anemia and cerebral perfusion in cases of suspected intrauterine growth restriction (IUGR).
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. PSV increases with gestational age due to progressive increase in fetal cardiac output and improved vascular flow. In fetal anemia, the reduced oxygen-carrying capacity of blood triggers compensatory cerebral vasodilation and increased cardiac output, resulting in elevated PSV. An elevated MCA PSV (>1.5 multiples of the median, MoM) is a sensitive marker for detecting moderate-to-severe fetal anemia. Conversely, in severe IUGR with hypoxia, PSV may be low or normal as the fetus attempts to conserve energy.
As gestation advances from 20 to 40 weeks, the fetal heart becomes more efficient, cardiac output increases, and PSV progressively increases. PSV values must be interpreted in the context of gestational age-specific nomograms.
• 20 weeks: ~35–45 cm/s (developing circulation, lower velocities)
• 28 weeks: ~50–65 cm/s (increasing with fetal growth)
• 34 weeks: ~65–80 cm/s
Measuring technique for PSV:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA.
4. Adjust the angle of insonation as close to 0° as possible — angle correction is critical for PSV measurements.
5. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
6. On each waveform, identify the highest peak of the systolic envelope and record the velocity value.
7. Take the mean of 3 measurements for reporting.
8. Always note the angle of insonation used in the report, as small angle variations significantly affect PSV values.
Normal PSV Reference Values for MCA by Gestational Age
| GA (weeks) | PSV (cm/s, 5th–95th centile) | Interpretation |
|---|---|---|
| 20 | 35–48 | Developing circulation; lower velocities |
| 22 | 40–52 | Progressive increase with fetal growth |
| 24 | 45–58 | Continued increase in flow velocity |
| 26 | 50–63 | Cardiac output improving |
| 28 | 54–68 | Significant increase in PSV |
| 30 | 58–73 | Steady rise in velocity |
| 32 | 62–78 | Fetal circulation maturing |
| 34 | 66–83 | — |
| 36 | 70–88 | — |
| 38 | 74–93 | — |
| 40 | 78–98 | Peak velocities at term |
| 41–42 | 80–100 | Stable post-term values |
Abnormal patterns:
• PSV > 1.5 MoM (multiples of the median) for GA → Elevated peak systolic velocity; indicates increased cerebral blood flow. Highly sensitive for detecting fetal anemia.
• PSV > 1.3 MoM for GA → Borderline elevated; mild anemia or early compensatory response to hypoxia.
• PSV < 5th centile for GA → Reduced peak systolic velocity; indicates decreased cardiac output or severe compromise. May indicate severe IUGR, cardiac dysfunction, or terminal fetal status.
• PSV normal or low with elevated UA PI/RI → Suggests severe IUGR with failed compensatory mechanism; indicates critical fetal status.
• Progressively rising PSV on serial scans → Progressive increase in cerebral blood flow; indicates worsening anemia or hypoxia with increasing compensatory response.
• Rapidly declining PSV on serial scans → Acute decrease in cardiac output; indicates fetal decompensation and critical compromise.
Clinical significance and advantages of PSV:
Unlike ratio-based indices (S/D, RI, PI), PSV is an absolute velocity measurement that directly reflects blood flow speed and cardiac output. PSV is highly sensitive for detecting fetal anemia — a PSV > 1.5 MoM has near-100% sensitivity for moderate-to-severe anemia (hemoglobin < 7 g/dL). PSV assessment is particularly valuable in Rh-alloimmunized pregnancies, fetomaternal hemorrhage, or suspected hemolytic disease where anemia is a primary concern. However, PSV is angle-dependent and requires strict attention to measurement technique. PSV is best used in conjunction with other Doppler parameters (RI, PI, mean velocity) for comprehensive hemodynamic assessment.
Clinical Decision Thresholds (MCA PSV)
| MCA PSV Finding | Hemodynamic Status | Clinical Interpretation | Clinical Action |
|---|---|---|---|
| Within normal range for GA | Normal | Normal cardiac output; adequate cerebral perfusion | Routine surveillance |
| 1.3–1.5 MoM | Borderline elevated | Mild anemia or early compensatory response; borderline cardiac output increase | Serial Doppler every 1–2 weeks; assess for anemia risk factors; consider middle cerebral artery sampling (cordocentesis) if high suspicion |
| > 1.5 MoM | Significantly elevated | Moderate-to-severe fetal anemia (Hb likely < 7 g/dL); compensatory increase in cardiac output | URGENT: Immediate fetal assessment; consider cordocentesis for confirmation; plan transfusion if appropriate; deliver if ≥34 weeks with confirmed anemia |
| > 1.8 MoM | Critically elevated | Severe anemia with maximal compensatory response; at risk for decompensation | EMERGENCY: Urgent cordocentesis; plan immediate intrauterine transfusion (IUT); daily CTG; prepare for delivery if decompensation signs (hydrops, cardiac failure) |
| < 5th centile for GA | Severely reduced | Low cardiac output; indicates severe compromise, IUGR, or cardiac dysfunction | URGENT: Assess all Doppler parameters (UA, MCA, DV); evaluate for cardiac anomalies; daily CTG; consider delivery if ≥34 weeks |
| PSV low with abnormal UA PI | Critical compromise | Severe IUGR with failed compensatory mechanism; imminent decompensation | EMERGENCY: Daily CTG; assess DV Doppler; urgent delivery if ≥32 weeks |
| Progressively rising PSV | Worsening anemia/hypoxia | Progressive compensatory response; indicates worsening fetal status | Serial Doppler; urgent evaluation for cause (anemia, hypoxia); prepare for intervention if confirmed |
| Rapidly declining PSV | Acute decompensation | Acute decrease in cardiac output; indicates critical fetal status | EMERGENCY: Immediate assessment; urgent delivery consideration; prepare for neonatal resuscitation |
PSV measurement and interpretation guidelines:
Measurement technique critical points:
• Angle of insonation: Must be as close to 0° as possible; even 10° angle error can result in 15% error in PSV value.
• Consistent measurement location: Always measure at M1 segment; proximal MCA near Circle of Willis.
• Sample volume placement: Center sample volume in vessel lumen; avoid vessel walls.
• Baseline adjustment: Ensure baseline is set correctly; misalignment causes systematic errors.
Nomogram selection and MoM calculation:
• Use gestational-age-specific nomograms: PSV increases significantly with advancing gestation (35–45 cm/s at 20 weeks to 78–98 cm/s at 40 weeks).
• Calculate MoM (multiples of the median): MoM = Measured PSV ÷ Median PSV for GA.
• MoM approach superior to absolute values: Accounts for normal physiologic variation with gestation; provides standardized interpretation.
• Always report both absolute PSV and MoM in clinical assessment.
PSV in anemia detection:
• PSV > 1.5 MoM: Sensitivity ~100% for moderate-to-severe anemia; specificity ~75–80%
• PSV 1.3–1.5 MoM: Sensitivity lower; overlap between normal and mild anemia; requires clinical correlation
• PSV within normal range does NOT exclude anemia: Mild anemia may not elevate PSV; clinical context essential
• In Rh disease: Serial PSV assessment superior to periodic measurements; rising trend indicates progressive anemia
PSV in IUGR and hypoxia assessment:
• Low PSV with elevated UA PI: Indicates severe IUGR with reduced cardiac output; poor prognosis
• Normal PSV with elevated UA PI: Early IUGR with maintained cardiac compensation; better prognosis
• PSV declining with worsening UA Doppler: Indicates progression to decompensation; imminent delivery needed
PSV-guided clinical management and decision points:
In Rh-alloimmunized pregnancies:
• PSV > 1.5 MoM → Cordocentesis for confirmation of anemia
• Confirmed anemia Hb < 7 g/dL → Intrauterine transfusion (IUT)
• Serial PSV trending → Guides timing of repeat IUT
At ≥34 weeks gestation:
• PSV > 1.5 MoM + confirmed anemia → Delivery recommended
• PSV > 1.8 MoM + signs of cardiac compromise → Immediate delivery
• PSV < 5th centile + abnormal UA Doppler → Delivery recommended
At 32–33 weeks gestation:
• PSV > 1.8 MoM → Urgent assessment; consider delivery if other signs of compromise
• PSV borderline elevated + Rh disease → Cordocentesis for definitive diagnosis
• Progressive PSV rise on serial scans → More frequent monitoring; prepare for intervention
Before 32 weeks gestation:
• PSV > 1.5 MoM in Rh disease → Cordocentesis + consider IUT
• Isolated PSV elevation without other abnormalities → Serial monitoring every 3–5 days
• Progressive rise in PSV → More aggressive intervention planning
Key points to remember:
• MCA PSV increases with advancing gestation (normal trend from ~40 cm/s at 20 weeks to ~85 cm/s at 40 weeks).
• PSV is angle-dependent — maintain angle of insonation <0° and be consistent for reproducible measurements.
• Always use MoM (multiples of median) rather than absolute PSV values; accounts for gestational-age variation.
• PSV > 1.5 MoM has ~100% sensitivity for moderate-to-severe anemia; use for screening in at-risk populations.
• Isolated PSV elevation does not diagnose anemia; requires clinical context and other assessment methods (cordocentesis).
• Measure on the M1 segment of MCA, proximal to branching, maintaining consistent technique.
• Serial PSV assessment superior to single measurements — trending over time detects progressive changes and guides intervention timing.
• Combine PSV with other Doppler parameters (RI, PI, EDV, UA Doppler, DV Doppler) for comprehensive hemodynamic evaluation.
• PSV is particularly valuable in Rh-alloimmunized pregnancies, fetomaternal hemorrhage, and hemolytic disease.
• PSV declining rapidly is alarming — indicates acute decompensation and requires urgent intervention.
• PSV normal or low with abnormal placental Doppler suggests IUGR, not anemia; indicates need for delivery planning.
EDV (End-Diastolic Velocity) → EDV (End-Diastolic Velocity) is the minimum blood flow velocity at the end of ventricular diastole in the middle cerebral artery. Unlike ratio-based indices (S/D, RI, PI), EDV is an absolute velocity measurement that directly reflects the baseline diastolic flow and is highly dependent on angle of insonation. EDV is increasingly used to assess fetal anemia and cerebral perfusion in cases of suspected intrauterine growth restriction (IUGR) and fetal hypoxia.
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. EDV increases with gestational age due to progressive reduction in cerebral vascular resistance and improved forward diastolic flow. In fetal anemia, the reduced oxygen-carrying capacity of blood triggers compensatory cerebral vasodilation and increased cardiac output, resulting in elevated EDV. An elevated MCA EDV reflects increased diastolic flow and is a marker of fetal anemia and increased cerebral perfusion.
Conversely, in severe IUGR with hypoxia and poor cardiac function, EDV may be low or absent as the fetus struggles to maintain adequate perfusion.
As gestation advances from 20 to 40 weeks, the cerebral vascular bed matures, resistance falls, and EDV progressively increases. EDV values must be interpreted in the context of gestational age-specific nomograms and in conjunction with PSV to calculate resistance indices.
• 20 weeks: ~10–15 cm/s (high resistance, minimal diastolic flow)
• 28 weeks: ~20–28 cm/s (diastolic flow improving)
• 34 weeks: ~28–35 cm/s
Measuring technique for EDV:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA.
4. Adjust the angle of insonation as close to 0° as possible — angle correction is critical for EDV measurements.
5. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
6. On each waveform, identify the lowest point of the diastolic envelope (the point just before the next systolic rise) and record the velocity value.
7. Take the mean of 3 measurements for reporting.
8. Always note the angle of insonation used in the report, as small angle variations significantly affect EDV values.
Normal EDV Reference Values for MCA by Gestational Age
| GA (weeks) | EDV (cm/s, 5th–95th centile) | Interpretation |
|---|---|---|
| 20 | 8–16 | High resistance; minimal diastolic flow |
| 22 | 10–18 | Diastolic flow beginning to increase |
| 24 | 12–21 | Progressive increase in diastolic velocity |
| 26 | 14–24 | Resistance gradually falling |
| 28 | 16–28 | Significant increase in diastolic flow |
| 30 | 19–32 | Steady rise in diastolic velocity |
| 32 | 22–36 | Cerebral circulation maturing |
| 34 | 25–40 | — |
| 36 | 28–43 | — |
| 38 | 31–47 | — |
| 40 | 34–51 | High diastolic flow at term |
| 41–42 | 36–53 | Stable post-term values |
Abnormal patterns:
• EDV > 95th centile for GA → Elevated end-diastolic velocity; indicates increased diastolic flow and cerebral vasodilation. Reflects brain-sparing effect in response to hypoxia or anemia.
• EDV < 5th centile for GA → Reduced end-diastolic velocity; indicates decreased diastolic flow and high cerebral vascular resistance. Suggests inadequate cerebral vascular maturation or primary cerebral compromise.
• EDV progressively rising on serial scans → Progressive increase in diastolic flow; indicates worsening anemia or hypoxia with increasing compensatory cerebral vasodilation.
• EDV progressively declining on serial scans → Progressive decrease in diastolic flow; indicates deteriorating cerebral perfusion and increasing vascular resistance.
• Elevated EDV with normal PSV → Unusual pattern; suggests selective diastolic flow increase; evaluate for specific hemodynamic disturbances.
• EDV markedly elevated with elevated PSV → Indicates uniform increase in flow across cardiac cycle; consistent with high-output state (anemia, hypoxia with compensation).
Clinical significance and advantages of EDV:
Unlike ratio-based indices (S/D, RI, PI), EDV is an absolute velocity measurement that directly reflects diastolic cerebral blood flow. EDV is sensitive for detecting cerebral vasodilation that occurs with fetal anemia, hypoxia, and IUGR with brain-sparing effect. Elevated EDV with elevated PSV indicates a high-output compensatory state typical of fetal anemia or acute hypoxia. Conversely, reduced EDV with low PSV indicates low-output failure associated with severe IUGR or cardiac dysfunction—a poor prognostic sign. EDV is angle-dependent and requires strict attention to measurement technique. EDV is best used in conjunction with PSV and other Doppler parameters to characterize the pattern of flow disturbance and guide clinical management.
Clinical Decision Thresholds (MCA EDV)
| MCA EDV Finding | Cerebral Hemodynamic Status | Clinical Interpretation | Clinical Action |
|---|---|---|---|
| Within normal range for GA | Normal | Normal cerebral diastolic flow; adequate vascular maturation | Routine surveillance |
| > 95th centile for GA | Elevated diastolic flow | Cerebral vasodilation; brain-sparing effect; indicates compensation to hypoxia or anemia | Urgent evaluation; assess PSV, RI, PI for pattern; evaluate for fetal anemia (check PSV for MoM); assess UA Doppler for placental insufficiency |
| > 95th centile + PSV > 1.5 MoM | High-output state | Elevated flow throughout cardiac cycle; consistent with moderate-to-severe fetal anemia or acute hypoxia | URGENT: Consider cordocentesis for anemia confirmation; plan intervention (transfusion or delivery) if confirmed |
| > 95th centile + PSV normal/low | Selective diastolic increase | Unusual pattern; may indicate specific vascular disturbance or measurement artifact; evaluate carefully | Repeat measurement with angle verification; assess all other Doppler parameters; consider other causes of flow disturbance |
| < 5th centile for GA | Reduced diastolic flow | High cerebral vascular resistance; inadequate vasodilation; suggests delayed maturation or compromise | Evaluate for IUGR; assess UA Doppler, RI, PI; serial monitoring; consider delivery if ≥34 weeks with growth restriction |
| < 5th centile + PSV < 5th centile | Low-output state | Reduced flow throughout cardiac cycle; indicates severe compromise, cardiac dysfunction, or terminal status | URGENT: Assess all Doppler parameters (UA, MCA, DV); evaluate for cardiac anomalies; daily CTG; urgent delivery if ≥32 weeks |
| EDV progressively rising | Worsening vasodilation | Progressive increase in cerebral diastolic flow; indicates worsening anemia or hypoxia with increasing compensatory response | Serial Doppler every 3–5 days; investigate cause (anemia, hypoxia); prepare for urgent intervention if rapid rise |
| EDV progressively declining | Worsening resistance | Progressive decrease in cerebral diastolic flow; indicates deteriorating cerebral perfusion and increasing resistance | Urgent assessment; evaluate all Doppler parameters; prepare for delivery if ≥32 weeks with concerning pattern |
EDV patterns and flow classification:
High-output flow pattern (anemia/acute hypoxia):
• Elevated EDV + Elevated PSV + Elevated mean velocity → High-output compensatory state
• Clinical context: Fetal anemia, acute hypoxia, or high-output cardiac state
• Associated findings: Low RI/PI; PSV > 1.5 MoM; may have elevated UA PI (placental insufficiency)
• Management: Confirm anemia with cordocentesis if indicated; plan transfusion or delivery
Low-output flow pattern (IUGR/cardiac dysfunction):
• Reduced EDV + Reduced PSV + Reduced mean velocity → Low-output failure state
• Clinical context: Severe IUGR, cardiac dysfunction, or imminent decompensation
• Associated findings: Elevated RI/PI; elevated UA PI; may have abnormal DV Doppler
• Management: Urgent delivery if ≥32 weeks; assess for cardiac anomalies; prepare for intensive neonatal care
Discordant flow pattern (selective diastolic abnormality):
• Elevated EDV + Normal PSV or Reduced EDV + Normal PSV → Unusual pattern
• Clinical context: Rare; may indicate measurement artifact, specific vascular lesion, or unusual hemodynamic state
• Management: Verify measurement technique; repeat with angle verification; assess for technical error before diagnosing pathology
EDV measurement and interpretation guidelines:
Measurement technique critical points:
• Angle of insonation: Must be as close to 0° as possible; even 10° angle error can result in 15–20% error in EDV value.
• Identify end-diastolic point: Point just before next systolic rise; not the trough of any diastolic notch if present.
• Sample volume placement: Center in vessel lumen; avoid vessel walls or turbulent flow regions.
• Baseline adjustment: Critical for accurate diastolic measurement; misalignment causes systematic errors in low-velocity measurements.
EDV in anemia detection:
• Elevated EDV with elevated PSV (>1.5 MoM): Consistent with anemia; high-output compensatory state
• EDV > 95th centile + PSV normal: Less specific; may represent partial compensation or non-anemic cause
• Serial EDV rising + PSV rising: Progressive anemia; requires intervention planning
• Isolated EDV elevation without PSV elevation: Consider measurement error; verify with repeat scan
EDV in IUGR and placental insufficiency:
• Low EDV with elevated UA PI: Indicates brain-sparing effect inadequate; concerning for IUGR
• Progressive EDV decline + rising UA PI: Indicates deteriorating fetal status; urgent delivery needed
• EDV < 5th centile + low PSV: Indicates severe compromise; poor prognosis
Cerebroplacental hemodynamic patterns using EDV:
• High EDV (>95th) + High UA EDV (>95th): Both high-output state; unusual; evaluate for systemic causes
• High EDV (>95th) + Low UA EDV (<5th): Classic brain-sparing pattern; cerebral vasodilation with placental insufficiency
• Low EDV (<5th) + Low UA EDV (<5th): Universal low-output state; severe compromise; poor prognosis
• Low EDV (<5th) + High UA EDV (>95th): Paradoxical pattern; rare; evaluate for measurement error or unusual pathology
EDV-guided clinical management and decision points:
At ≥34 weeks gestation:
• EDV > 95th centile + PSV > 1.5 MoM + confirmed anemia → Delivery recommended
• EDV < 5th centile + abnormal UA Doppler → Delivery recommended
• EDV progressively declining + UA PI rising → Urgent delivery
At 32–33 weeks gestation:
• EDV > 95th centile + PSV > 1.5 MoM → Cordocentesis for anemia confirmation; prepare for intervention
• EDV < 5th centile + elevated UA PI → Daily CTG; consider delivery if other signs of compromise
• EDV progressively changing (rising or declining) → Intensive surveillance every 3–5 days
Before 32 weeks gestation:
• EDV > 95th centile + PSV > 1.5 MoM in Rh disease → Cordocentesis; consider intrauterine transfusion
• Isolated EDV abnormality without other findings → Serial monitoring every 5–7 days
• Progressive EDV change → More frequent assessments; consider earlier intervention
Key points to remember:
• MCA EDV increases with advancing gestation (normal trend from ~10 cm/s at 20 weeks to ~40 cm/s at 40 weeks).
• EDV is angle-dependent — maintain angle of insonation <0° and be consistent for reproducible measurements.
• Always interpret MCA EDV against gestational-age-specific centiles, not absolute values.
• EDV pattern (elevated vs. reduced) must be interpreted with PSV to determine flow state (high-output vs. low-output).
• Elevated EDV + Elevated PSV = High-output state (anemia or acute hypoxia); indicates compensatory mechanism.
• Reduced EDV + Reduced PSV = Low-output state (IUGR or cardiac dysfunction); indicates failure of compensation.
• Measure on the M1 segment of MCA, proximal to branching, maintaining consistent technique.
• Serial EDV assessment superior to single measurements — trending over time detects progressive changes and guides intervention timing.
• Combine EDV with PSV, RI, PI, and UA Doppler for comprehensive hemodynamic characterization.
• EDV is particularly valuable for distinguishing anemia (high EDV + high PSV) from IUGR (low EDV + low PSV).
• Rapidly rising EDV is concerning — indicates acute worsening of anemia or hypoxia; requires urgent intervention planning.
• Rapidly declining EDV is alarming — indicates acute deterioration in cerebral perfusion; requires immediate assessment and urgent delivery.
• Use EDV in context of complete Doppler profile (MCA RI/PI, PSV, mean velocity, UA Doppler, DV Doppler) for optimal clinical decision-making.
Mean Velocity (MV) → Mean Velocity (MV) is the average blood flow velocity throughout the entire cardiac cycle in the middle cerebral artery. It is calculated as the area under the Doppler waveform envelope divided by the cardiac cycle duration. Unlike ratio-based indices (S/D, RI, PI), mean velocity is an absolute velocity measurement that directly reflects overall blood flow and is highly dependent on angle of insonation. Mean velocity is used in conjunction with PSV and EDV to calculate resistance indices and to assess fetal cerebral perfusion and cardiac output.
Formula:
Mean Velocity (MV) = Area under the velocity-time waveform ÷ Cardiac cycle duration
Approximate MV ≈ (S + 2D) ÷ 3 (simplified estimation)
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. Mean velocity increases with gestational age due to progressive increase in fetal cardiac output and improved cerebral perfusion. Mean velocity reflects the integrated flow throughout the entire cardiac cycle, providing a comprehensive view of cerebral hemodynamics.
In fetal anemia, the reduced oxygen-carrying capacity of blood triggers compensatory cerebral vasodilation and increased cardiac output, resulting in elevated mean velocity. Mean velocity is particularly useful in calculating the Pulsatility Index (PI), which is derived from the formula: PI = (S - D) ÷ MV.
Conversely, in severe IUGR with hypoxia and poor cardiac function, mean velocity may be low or reduced as the fetus attempts to conserve energy and reduce metabolic demands.
As gestation advances from 20 to 40 weeks, the fetal heart becomes more efficient, cardiac output increases, and mean velocity progressively increases. Mean velocity values must be interpreted in the context of gestational age-specific nomograms.
• 20 weeks: ~20–28 cm/s (developing circulation, lower velocities)
• 28 weeks: ~32–45 cm/s (increasing with fetal growth)
• 34 weeks: ~42–55 cm/s
Measuring technique for Mean Velocity:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA.
4. Adjust the angle of insonation as close to 0° as possible — angle correction is critical for mean velocity measurements.
5. Measure during fetal rest (no breathing / movement), capture at least 3 uniform waveforms.
6. Most ultrasound machines automatically calculate the mean velocity from the velocity-time integral (the area enclosed by the Doppler waveform).
7. Take the mean of 3 measurements for reporting.
8. Always note the angle of insonation used in the report, as small angle variations significantly affect mean velocity values.
9. Mean velocity is essential for calculating PI (Pulsatility Index) and for comprehensive hemodynamic assessment.
Normal Mean Velocity Reference Values for MCA by Gestational Age
| GA (weeks) | Mean Velocity (cm/s, 5th–95th centile) | Interpretation |
|---|---|---|
| 20 | 19–30 | Developing circulation; lower velocities |
| 22 | 21–33 | Progressive increase with fetal growth |
| 24 | 24–37 | Continued increase in flow velocity |
| 26 | 27–41 | Cardiac output improving |
| 28 | 30–47 | Significant increase in mean velocity |
| 30 | 33–51 | Steady rise in velocity |
| 32 | 36–55 | Fetal circulation maturing |
| 34 | 40–59 | — |
| 36 | 43–63 | — |
| 38 | 47–68 | — |
| 40 | 50–72 | Peak mean velocities at term |
| 41–42 | 52–75 | Stable post-term values |
Abnormal patterns:
• Mean Velocity > 95th centile for GA → Elevated mean velocity throughout cardiac cycle; indicates increased cardiac output and cerebral blood flow. Reflects high-output compensatory state in response to hypoxia or anemia.
• Mean Velocity < 5th centile for GA → Reduced mean velocity throughout cardiac cycle; indicates decreased cardiac output and cerebral perfusion. Suggests severe IUGR, cardiac dysfunction, or critical fetal compromise.
• Mean Velocity progressively rising on serial scans → Progressive increase in overall cerebral blood flow; indicates worsening anemia or hypoxia with increasing compensatory cardiac output.
• Mean Velocity progressively declining on serial scans → Progressive decrease in overall cerebral blood flow; indicates deteriorating cardiac function and fetal status.
• Elevated Mean Velocity with elevated PSV and EDV → Uniform increase in flow throughout cardiac cycle; consistent with high-output state typical of fetal anemia or acute hypoxia.
• Reduced Mean Velocity with reduced PSV and EDV → Uniform decrease in flow throughout cardiac cycle; consistent with low-output failure associated with severe IUGR or cardiac dysfunction.
Clinical significance and advantages of Mean Velocity:
Unlike ratio-based indices (S/D, RI, PI), mean velocity is an absolute velocity measurement that directly reflects the integrated blood flow throughout the entire cardiac cycle. Mean velocity is essential for calculating Pulsatility Index (PI) and provides a comprehensive view of overall cerebral perfusion independent of waveform morphology. Mean velocity is particularly sensitive for detecting global changes in cardiac output and is useful for distinguishing between hemodynamic states: elevated mean velocity indicates high-output compensation (anemia, hypoxia), while reduced mean velocity indicates low-output failure (severe IUGR, cardiac dysfunction). Mean velocity is angle-dependent and requires strict attention to measurement technique. Mean velocity is best used in conjunction with PSV, EDV, and resistance indices to characterize the complete hemodynamic profile and guide clinical management.
Clinical Decision Thresholds (MCA Mean Velocity)
| MCA Mean Velocity Finding | Cardiac Output Status | Clinical Interpretation | Clinical Action |
|---|---|---|---|
| Within normal range for GA | Normal | Normal cardiac output; adequate cerebral perfusion throughout cycle | Routine surveillance |
| > 95th centile for GA | Elevated cardiac output | Increased flow throughout cardiac cycle; high-output compensatory state; indicates response to hypoxia or anemia | Urgent evaluation; assess PSV/EDV for pattern; evaluate for fetal anemia (check PSV for MoM); assess UA Doppler for placental insufficiency |
| > 95th centile + PSV > 1.5 MoM + EDV > 95th | Marked high-output | Significant increase in flow throughout cycle; consistent with moderate-to-severe fetal anemia or acute hypoxia | URGENT: Consider cordocentesis for anemia confirmation; plan intervention (transfusion or delivery) if confirmed |
| > 95th centile + normal PI/RI | Elevated flow; preserved resistance | Increased cardiac output without proportional vasodilation; unusual pattern; suggests specific hemodynamic disturbance | Evaluate for causes (anemia without typical vasodilation, hypoplastic left heart, other cardiac lesions); serial assessment |
| < 5th centile for GA | Reduced cardiac output | Decreased flow throughout cycle; indicates poor cardiac function or severe compromise; suggests low-output failure | Evaluate for IUGR, cardiac anomalies; assess UA Doppler, RI, PI, DV Doppler; daily CTG; consider delivery if ≥34 weeks |
| < 5th centile + PSV < 5th + EDV < 5th | Severe low-output | Marked reduction in flow throughout cycle; indicates severe cardiac dysfunction or imminent decompensation | URGENT: Assess all Doppler parameters (UA, MCA, DV); evaluate for cardiac anomalies; daily CTG; urgent delivery if ≥32 weeks |
| Mean Velocity progressively rising | Increasing cardiac output | Progressive increase in overall cerebral blood flow; indicates worsening anemia or hypoxia with increasing compensatory response | Serial Doppler every 3–5 days; investigate cause (anemia, hypoxia); assess PSV trending; prepare for urgent intervention if rapid rise |
| Mean Velocity progressively declining | Worsening cardiac output | Progressive decrease in overall cerebral blood flow; indicates deteriorating cardiac function and fetal status | Urgent assessment; evaluate all Doppler parameters; assess for cardiac dysfunction; prepare for delivery if ≥32 weeks with concerning pattern |
| Rapid Mean Velocity change (>10 cm/s) | Acute hemodynamic shift | Acute change in cardiac output; indicates significant acute event (hemorrhage, infection, decompensation) | EMERGENCY: Immediate comprehensive assessment; urgent delivery if ≥32 weeks; prepare for neonatal resuscitation |
Mean Velocity patterns and hemodynamic states:
High-output flow pattern (anemia/acute hypoxia):
• Elevated Mean Velocity + Elevated PSV + Elevated EDV + Low RI/PI → High-output compensatory state
• Magnitude: Mean Velocity > 95th centile; PSV > 1.5 MoM; EDV > 95th centile
• PI contribution: PI remains relatively low despite high absolute velocities because the normalized ratio accounts for proportional increase throughout cycle
• Clinical context: Fetal anemia, acute hypoxia, high-output cardiac state
• Associated findings: May have elevated UA PI (placental insufficiency); normal or elevated mean velocity in umbilical artery
• Management: Confirm anemia with cordocentesis if indicated; plan transfusion or delivery; serial mean velocity trending guides timing of intervention
Low-output flow pattern (IUGR/cardiac dysfunction):
• Reduced Mean Velocity + Reduced PSV + Reduced EDV + High RI/PI → Low-output failure state
• Magnitude: Mean Velocity < 5th centile; PSV < 5th centile; EDV < 5th centile
• PI contribution: PI may be normal or even relatively low despite low absolute velocities because the normalized ratio is preserved
• Clinical context: Severe IUGR, cardiac dysfunction, imminent decompensation
• Associated findings: Elevated UA PI; abnormal DV Doppler (reversed flow, absent flow); may have cardiac anomalies on ultrasound
• Management: Urgent delivery if ≥32 weeks; assess for cardiac anomalies; prepare for intensive neonatal care; poor prognosis
Preserved mean velocity with abnormal PI/RI (unusual pattern):
• Normal Mean Velocity + Elevated RI/PI + Low EDV → High resistance despite maintained mean flow
• Mechanism: Reduced diastolic flow offset by increased systolic flow; results in relatively preserved mean but abnormal resistance indices
• Clinical interpretation: Early or developing resistance increase; possible transition state between compensation and decompensation
• Management: Serial monitoring; assess for progression to true low-output state
Elevated mean velocity with elevated resistance indices (paradoxical pattern):
• Elevated Mean Velocity + Elevated RI/PI → Unusual combination; suggests specific pathology
• Possible causes: Measurement error, unusual waveform morphology, specific vascular lesions
• Management: Verify measurement technique with angle verification; repeat if questionable; assess for technical error before diagnosing pathology
Mean Velocity measurement and interpretation guidelines:
Measurement technique critical points:
• Angle of insonation: Must be as close to 0° as possible; angle error affects both PSV and EDV equally, but mean velocity calculation requires accurate envelope integration.
• Velocity-time integral (VTI): Mean velocity calculated from area under the Doppler waveform envelope divided by cardiac cycle duration.
• Waveform quality: Clear, well-defined envelope essential for accurate mean velocity calculation; poor signal degrades mean velocity accuracy.
• Sample volume placement: Center in vessel lumen; avoid vessel walls or turbulent flow regions that distort waveform.
• Baseline adjustment: Critical for accurate integration; misalignment affects mean velocity calculation significantly.
Mean velocity in cardiac output assessment:
• Mean velocity > 95th centile: Indicates increased cardiac output; consistent with fetal compensation to anemia or hypoxia
• Mean velocity < 5th centile: Indicates reduced cardiac output; concerning for cardiac dysfunction or severe compromise
• Serial mean velocity rising: Progressive increase in cardiac output; indicates worsening anemia or compensatory response
• Serial mean velocity declining: Progressive decrease in cardiac output; indicates deteriorating fetal status
Mean velocity in anemia detection:
• Elevated Mean Velocity + PSV > 1.5 MoM + Elevated EDV: Consistent with anemia; high-output compensatory state
• Mean Velocity borderline + PSV borderline: May represent mild anemia or early compensation; requires clinical correlation
• Serial mean velocity trending with PSV: Parallel changes suggest uniform high-output state; divergent changes suggest measurement error or unusual pattern
Mean velocity in IUGR and placental insufficiency:
• Low Mean Velocity with elevated UA PI: Indicates inadequate brain-sparing effect; concerning for severe IUGR
• Progressive Mean Velocity decline + rising UA PI: Indicates deteriorating fetal status and cardiac decompensation; urgent delivery needed
• Mean Velocity < 5th centile + PSV normal: Unusual pattern; suggests selective reduction in flow averaging; evaluate for technical error
Mean Velocity and PI relationship:
• PI = (PSV - EDV) ÷ Mean Velocity
• Elevated Mean Velocity with low RI/PI: Indicates high-output state with appropriate vasodilation
• Reduced Mean Velocity with high RI/PI: Indicates low-output state with high resistance
• Mean Velocity critical for PI calculation: Errors in mean velocity measurement directly affect PI accuracy
Mean Velocity-guided clinical management and decision points:
At ≥34 weeks gestation:
• Mean Velocity > 95th centile + PSV > 1.5 MoM + confirmed anemia → Delivery recommended
• Mean Velocity < 5th centile + abnormal UA Doppler → Delivery recommended
• Mean Velocity progressively declining + UA PI rising → Urgent delivery
• Rapid Mean Velocity change → Immediate delivery consideration
At 32–33 weeks gestation:
• Mean Velocity > 95th centile + PSV > 1.5 MoM → Cordocentesis for anemia confirmation; prepare for intervention
• Mean Velocity < 5th centile + elevated UA PI → Daily CTG; consider delivery if other signs of compromise present
• Mean Velocity progressively changing (rising or declining) → Intensive surveillance every 3–5 days; prepare for intervention
Before 32 weeks gestation:
• Mean Velocity > 95th centile + PSV > 1.5 MoM in Rh disease → Cordocentesis; consider intrauterine transfusion
• Isolated Mean Velocity abnormality without other findings → Serial monitoring every 5–7 days
• Progressive Mean Velocity change → More frequent assessments; consider earlier intervention
Cerebroplacental hemodynamic patterns using Mean Velocity:
• High MCA Mean Velocity + Normal UA Mean Velocity: Cerebral high-output state; suggests brain-sparing effect
• High MCA Mean Velocity + High UA Mean Velocity: Global high-output state; suggests systemic compensation (severe anemia, hypoxia)
• Low MCA Mean Velocity + Low UA Mean Velocity: Global low-output state; severe compromise; poor prognosis
• Low MCA Mean Velocity + Normal UA Mean Velocity: Selective cerebral reduction; suggests primary cerebral compromise or cardiac dysfunction
Key points to remember:
• MCA Mean Velocity increases
Diastolic Notch → Diastolic Notch is a brief reversal or deceleration of blood flow velocity during mid-to-late diastole in the middle cerebral artery waveform. It appears as a characteristic dip or indentation in the descending limb of the Doppler waveform, typically occurring in early gestation and progressively disappearing as pregnancy advances. The presence or absence of a diastolic notch can provide qualitative information about cerebral vascular resistance, vascular maturation, and fetal hemodynamic status.
What it measures:
The middle cerebral artery supplies oxygenated blood to the fetal brain. A diastolic notch represents transient flow deceleration caused by the compliance mismatch between the proximal cerebral vessels and the distal vascular bed during early gestation. The notch reflects high vascular resistance in the distal cerebral circulation.
As gestation advances and the cerebral vascular bed matures through progressive vasodilation and angiogenesis, the vascular compliance improves, resistance decreases, and the diastolic notch progressively smooths out and disappears.
In IUGR with placental insufficiency and fetal hypoxia, the normal progression of notch disappearance may be delayed or the notch may persist abnormally, suggesting inadequate cerebral vascular maturation or persistent high resistance. However, the presence of a diastolic notch in early gestation is NORMAL and expected.
Conversely, in fetal anemia, the cerebral vasculature undergoes vasodilation and the notch may disappear prematurely or be absent from the outset, reflecting low resistance and increased diastolic flow.
• Early gestation (20–24 weeks): Diastolic notch PRESENT (normal finding)
• Mid-gestation (26–30 weeks): Notch progressively disappearing
• Late gestation (32+ weeks): Notch typically ABSENT (smooth diastolic flow)
Measuring technique for Diastolic Notch assessment:
1. Obtain a transverse section of the fetal head at the level of the biparietal diameter (BPD).
2. Identify the circle of Willis with color Doppler; locate the M1 segment of the MCA (proximal portion after branching from the internal carotid artery).
3. Place PW Doppler sample volume (2–3 mm) over the MCA with angle of insonation close to 0°.
4. Measure during fetal rest (no breathing / movement), capture at least 2–3 clear waveforms.
5. Examine the descending limb (diastolic portion) of the waveform carefully for any visible dip, notch, or reversal pattern.
6. Note whether a notch is present, absent, or borderline.
7. If present, assess the depth and timing of the notch in relation to the cardiac cycle.
8. Always correlate with gestational age — notch presence must be interpreted in context of normal gestation-dependent progression.
9. Serial assessment can help track vascular maturation and detect abnormal patterns.
Diastolic Notch Presence by Gestational Age
| GA (weeks) | Expected Notch Status | Interpretation |
|---|---|---|
| 20–22 | PRESENT (common) | Normal high-resistance cerebral circulation |
| 23–25 | PRESENT (common) | Expected finding; notch beginning to smooth |
| 26–28 | PRESENT or BORDERLINE | Transitional phase; progressive disappearance |
| 29–31 | BORDERLINE or ABSENT | Normal vascular maturation in progress |
| 32–34 | ABSENT (expected) | Mature cerebral circulation; smooth waveform |
| 35–40 | ABSENT (expected) | Established low-resistance circulation |
| 41–42 | ABSENT (expected) | Stable post-term waveform morphology |
• Notch persisting beyond 32 weeks → Delayed disappearance of diastolic notch; indicates inadequate cerebral vascular maturation or resistance abnormality. May suggest IUGR, growth restriction, or placental insufficiency.
• Notch abnormally prominent or deep → Exaggerated flow deceleration in mid-to-late diastole; may indicate transient hemodynamic disturbances or specific vascular abnormalities.
• Notch absent prematurely (before 20 weeks) → Early disappearance of diastolic notch; unusual finding; may indicate abnormal cerebral vascular development or measurement artifact.
• Notch re-appearing on serial scans → Reappearance of previously absent notch in late gestation; rare finding; may indicate acute hemodynamic changes or vascular disturbance.
• Abnormal notch morphology → Notch with unusual shape, timing, or depth; may indicate specific flow patterns or vascular lesions.
• Notch present with elevated RI/PI/S/D → Persistent notch associated with high cerebral vascular resistance; indicates delayed vascular maturation and inadequate cerebral compensation.
• Notch present with low RI/PI/S/D → Unusual combination; notch present despite low resistance; may indicate unique hemodynamic state or measurement artifact.
Clinical significance of diastolic notch patterns:
The diastolic notch is a qualitative morphological feature of the MCA Doppler waveform that reflects vascular compliance and resistance maturation. Normal notch progression (present early, progressively smoothing, absent by 32 weeks) is reassuring and indicates normal cerebral vascular development. Abnormal notch patterns (persistence, delayed disappearance, re-appearance) may indicate delayed cerebral vascular maturation, IUGR, or placental insufficiency. The notch is best interpreted in conjunction with quantitative Doppler indices (RI, PI, S/D) and clinical context. Abnormal notch patterns warrant further evaluation with growth parameters, UA Doppler, and serial monitoring. The diastolic notch is more of a supportive qualitative finding than a primary diagnostic parameter; quantitative indices (RI, PI) are generally more reliable for clinical decision-making.
Clinical Decision Thresholds (MCA Diastolic Notch)
| MCA Diastolic Notch Finding | Vascular Maturation Status | Clinical Interpretation | Clinical Action |
|---|---|---|---|
| Present at 20–26 weeks (expected) | Normal maturation | High cerebral resistance; normal early-gestation finding; indicates developing circulation | Routine surveillance; note presence but not concerning |
| Progressively disappearing 26–32 weeks | Normal maturation in progress | Expected pattern; notch smoothing reflects decreasing resistance and normal vascular development | Routine surveillance; reassuring pattern; normal progression |
| Absent at ≥32 weeks (expected) | Mature circulation | Normal low-resistance cerebral circulation; vascular compliance fully developed | Routine surveillance |
| Persisting at 32–34 weeks | Delayed maturation | Notch still present beyond expected time; indicates slower-than-normal vascular maturation; possible IUGR or growth restriction | Evaluate biometry for growth restriction; assess RI/PI values; serial Doppler every 1–2 weeks; assess UA Doppler |
| Prominent/deep notch at any GA | Exaggerated resistance | Unusually pronounced flow deceleration; may indicate specific hemodynamic disturbance or vascular abnormality | Correlate with quantitative indices (RI, PI, S/D); assess for IUGR; serial monitoring |
| Persisting at ≥36 weeks | Significantly delayed maturation | Persistent notch in late gestation; abnormal finding; suggests significant IUGR or primary cerebral vascular compromise | URGENT: Evaluate growth parameters; assess RI/PI (should be low despite notch); serial Doppler; strongly consider delivery if ≥37 weeks or other concerning signs |
| Notch absent prematurely (<20 weeks) | Abnormal early development | Unusual finding; early notch disappearance; may indicate abnormal vascular development or primary cerebral pathology | Detailed fetal ultrasound for anomalies; assess RI/PI/PSV; serial assessment; investigate for underlying pathology |
| Re-appearing notch on serial scans | Abnormal hemodynamic change | Rare finding; reappearance of previously absent notch; may indicate acute hemodynamic disturbance or progressive pathology | URGENT: Comprehensive Doppler reassessment; evaluate for acute changes; daily CTG; consider delivery if ≥34 weeks |
Notch patterns and their clinical correlations:
Normal progressive notch pattern (reassuring):
• Pattern: Notch present at 20–26 weeks; progressively becomes shallower and smoother; absent by 32–34 weeks
• Associated findings: RI/PI/S/D values progressively decreasing with GA; PSV/EDV progressively increasing; normal growth trajectory
• Clinical significance: Normal cerebral vascular maturation; reflects expected progression of vascular development and decreasing resistance
• Management: Routine surveillance; reassuring finding; no intervention indicated
Delayed notch disappearance (abnormal pattern):
• Pattern: Notch still present at 32+ weeks when it should be absent; persistent beyond normal timeline
• Associated findings: RI/PI/S/D values elevated or not decreasing appropriately; may have growth restriction on biometry; may have elevated UA PI
• Clinical significance: Delayed cerebral vascular maturation; suggests inadequate vascular development or IUGR; indicates resistance not decreasing normally
• Management: Evaluate biometry for growth restriction; assess all Doppler parameters (RI, PI, S/D, UA Doppler); serial monitoring every 1–2 weeks; consider delivery if ≥34 weeks with confirmed growth restriction
Persistent notch with elevated RI/PI (concerning pattern):
• Pattern: Notch present beyond 32 weeks AND elevated RI/PI/S/D for GA
• Associated findings: Growth restriction common; elevated UA PI suggesting placental insufficiency; low PSV/EDV relative to GA
• Clinical significance: Combined evidence of delayed maturation and high resistance; indicates significant cerebral vascular compromise and inadequate fetal compensation
• Management: URGENT evaluation; strongly consider delivery if ≥34 weeks; prepare for possible early delivery; assess for IUGR-related complications
Persistent notch with low RI/PI (unusual pattern):
• Pattern: Notch present beyond 32 weeks BUT RI/PI/S/D values are low (opposite of expected)
• Possible explanation: Rare pattern; may indicate unusual hemodynamic state with selective diastolic disturbance; possible measurement artifact
• Clinical significance: Unclear; may represent transient flow phenomenon or specific vascular characteristic
• Management: Verify measurement technique; repeat assessment with careful angle verification; correlate with PSV/EDV; assess for technical error
Abnormally prominent/exaggerated notch:
• Pattern: Notch depth unusually marked; significant diastolic flow reversal or deceleration at any GA
• Associated findings: May have abnormal RI/PI; may have cardiac abnormalities; may have vascular lesions
• Clinical significance: May indicate transient hemodynamic disturbance, specific vascular abnormality, or measurement artifact
• Management: Correlate with quantitative indices; detailed fetal cardiac and cerebral ultrasound; serial assessment; investigate for underlying pathology
Early notch disappearance (notch absent before 20 weeks):
• Pattern: Diastolic notch not visible at 16–20 weeks when presence is expected
• Associated findings: Unusually low RI/PI for GA; elevated PSV/EDV; may have fetal anemia or other systemic condition
• Clinical significance: Unusual; suggests either early cerebral vasodilation or abnormal vascular development; requires investigation
• Management: Assess for fetal anemia (check PSV for MoM); detailed fetal ultrasound for anomalies; investigate for hemolytic disease or other pathology; serial assessment
Notch assessment technique and interpretation guidelines:
Optimal notch visualization:
• Waveform quality: Clear, well-defined Doppler envelope essential; poor signal obscures notch detection
• Sample placement: Proximal M1 segment provides best notch visualization; distal MCA may have less prominent notch
• Multiple waveforms: Assess at least 2–3 cardiac cycles; notch may vary slightly cycle-to-cycle
• Fetal state: Notch assessment during fetal rest (no breathing/movement) most reliable
Notch identification and documentation:
• Visual assessment: Identify dip or indentation in descending (diastolic) limb of waveform
• Timing: Notch occurs in mid-to-late diastole; just before end-diastolic point
• Depth: Record depth and prominence (shallow vs. deep/exaggerated)
• Documentation: Report as "present," "absent," "borderline," or "prominent/exaggerated"
• Serial notation: Compare with prior scans to assess progression pattern
Distinguishing notch from other waveform features:
• Diastolic notch: Transient reversal/deceleration in mid-to-late diastole; normal in early gestation
• End-diastolic flow reversal: Complete reversal (negative velocity) at end-diastole; abnormal even in early gestation; indicates severe resistance
• Diastolic oscillations: Multiple undulations in diastole; different from simple notch; may indicate turbulent flow
• Spectral broadening: Widened velocity envelope; different finding; indicates turbulence
Notch-guided clinical management and decision points:
At ≥36 weeks gestation:
• Notch still present → Delivery should be strongly considered, especially if ≥37 weeks
• Notch present + elevated RI/PI → Urgent delivery recommendation
• Notch present + growth restriction → Delivery recommended
At 32–35 weeks gestation:
• Notch persisting + normal RI/PI + normal growth → Serial Doppler every 1–2 weeks; deliver at 37+ weeks
• Notch persisting + elevated RI/PI → Consider delivery if other signs of compromise present
• Notch persisting + growth restriction + abnormal UA Doppler → Delivery consideration at 34+ weeks
Before 32 weeks gestation:
• Notch present (normal finding) + normal RI/PI + normal growth → Routine surveillance
• Notch persisting (abnormal for GA) → Serial Doppler assessment; prepare for possible early delivery decision
Serial notch assessment and prognostic significance:
• Notch progressively disappearing: Reassuring; normal vascular maturation; no intervention needed
• Notch static (not changing): Concerning; suggests failed normal maturation; warrants investigation
• Notch becoming more prominent: Unusual; may indicate deteriorating hemodynamics; requires urgent assessment
• Notch re-appearing after disappearance: Rare and concerning; suggests acute hemodynamic change; requires urgent evaluation
Key points to remember:
• Diastolic notch normal at 20–26 weeks; reflects high cerebral vascular resistance and developing circulation.
• Progressive notch smoothing 26–32 weeks is expected and indicates normal vascular maturation.
• Notch should be absent by 32–34 weeks in normal pregnancy.
• Notch persisting beyond 32 weeks is abnormal and suggests delayed vascular maturation or IUGR.
• Diastolic notch is a qualitative supportive finding; quantitative indices (RI, PI, S/D) are primary parameters for clinical decision-making.
• Correlate notch findings with quantitative Doppler indices — persistent notch should have elevated RI/PI for interpretation to be consistent.
• Notch presence alone is less predictive than combined assessment (notch + RI/PI + growth parameters + UA Doppler).
• Serial notch assessment more important than isolated finding — trend of progression/disappearance guides management decisions.
• Notch assessment should be part of comprehensive Doppler evaluation; integrate with S/D, RI, PI, PSV, EDV, mean velocity.
• Abnormal notch patterns warrant further investigation for IUGR, growth restriction, or other fetal compromise.
• Notch persisting at term ≥37 weeks + growth restriction or other abnormalities → Delivery recommended.
• Use notch as supportive evidence in context of complete clinical picture, not as sole indicator for intervention.
No comments:
Post a Comment