How to Measure Umbilical Artery S/D Ratio (Step-by-Step)

Umbilical Artery S/D Ratio

Fetal Doppler

Introduction

Umbilical artery Doppler is a key tool in fetal surveillance, especially in cases of suspected placental insufficiency and intrauterine growth restriction (IUGR). The S/D ratio reflects downstream placental resistance.

Patient Position

• Supine or slight left lateral position
• Use 3–5 MHz curvilinear probe

Sampling Technique

• Select a free-floating loop of umbilical cord


Free-floating loop [UC]

• Avoid fetal abdominal and placental insertion sites

• Use color Doppler for vessel identification
• Apply pulsed Doppler with angle ≤ 30°
• Sample gate: 1–2 mm

Waveform Criteria

• Obtain at least 3–5 uniform waveforms
• No fetal movement or breathing artifacts
• Clear systolic and diastolic components

Measurement

S/D ratio is calculated as:

S/D = Peak Systolic Velocity ÷ End Diastolic Velocity

Example

S = 40 cm/s, D = 10 cm/s → S/D = 4.0

Normal Values (Gestational Age)

Gestational Age (Weeks)	Normal S/D Ratio
20	< 5.0
24	< 4.5
28	< 4.0
30	< 3.8
32	< 3.6
34	< 3.4
36	< 3.2
38	< 3.0
40	< 3.0

Note: S/D ratio decreases with advancing gestational age due to reduced placental resistance.

What does high S/D ratio mean?

UCA Doppler

✖

UCA S/D Calculator

Systolic (S) Diastolic (D)

What does high S/D ratio mean?

UCA Doppler

Abnormal Findings

• Increased S/D ratio → placental resistance
• Absent end-diastolic flow (AEDF)
• Reversed end-diastolic flow (REDF)

Common Errors

• Wrong sampling site
• High Doppler angle
• Large sample volume
• Irregular waveform

Conclusion

Accurate S/D measurement requires proper technique, correct sampling site, and consistent waveform acquisition. It plays a vital role in fetal monitoring and clinical decision-making.

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Declaration

This content is intended for academic and educational purposes only.

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Ultrasound templates-Perineal and groin

PERINEAL & GROIN

📝 Perineal and groin Male

📝 Perineal and groin Female

─── 🧾 Perineal and groin male ──

Templates

▸

COUNSELING DAY

📄 Rt side Normal study

📄 Lt side Normal study

📄 BL side Normal study

📷 Insert Image

Patient Info

Fill fields and click Insert / Update to add a header to the report.

Name:

Age (years):

Sex: Female Male Other

Referring Doctor:

Date of Exam:

Width (%) Keep ratio

📝 No template loaded.

×

🔍 Search Saved Reports

✍️ Footer & Signatures

Technologist name Technologist title Consultant Doctor name Consultant title

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Footer alignment Technologist left — Doctor right Technologist right — Doctor left Footer font size (px) Vertical spacing above footer (px)

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End of Topic

You have reached the end of this First-Trimester Ultrasound topic.

Content is intended for educational, training, and clinical reference only.

Declaration:
I, R. K. Mouj, declare that the material presented in this Pediatric Perineal and Groin Ultrasound (Female) is intended solely for educational and academic purposes. All descriptions related to perineal and groin ultrasound technique, high-frequency probe positioning, evaluation of superficial soft tissues, inguinal canals, labial region assessment, lymph node evaluation, hernia assessment, canal of Nuck evaluation, abscess formation, sinus tract mapping, cystic and solid lesions, vascular assessment with Doppler, and example observations are illustrative in nature. Clinical examination, correlation with pediatric history, laboratory findings when indicated, other imaging modalities if required, institutional protocols, and professional medical judgment are essential before making any diagnostic or management decisions.

⬆ Back to Top

© SonoAcademy — an educational platform dedicated to simplifying diagnostic radiography and ultrasound imaging through practical tools, structured reporting guidance, and clinically focused learning.

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