Definition
The Empty sac sign describes a gestational sac visualized within the uterine cavity on ultrasound without a visible yolk sac or embryo when expected by gestational age or size. It is an early sonographic indicator of failed embryogenesis and may herald an anembryonic pregnancy (blighted ovum) when diagnostic criteria are met.
Images
Ultrasound Report - line
Example: "Intrauterine gestational sac measuring MSD __ mm. No yolk sac or embryo identified. Findings suspicious for anembryonic pregnancy — correlate with serial β-hCG and follow-up TVS."
Conclusion
Empty sac sign suggests possible anembryonic pregnancy. The mean sac diameter (MSD) is above diagnostic thresholds consider a diagnosis of failed early pregnancy in the appropriate clinical context.
Recommendation
Repeat transvaginal ultrasound in 7–10 days if equivocal and patient is clinically stable.
Serial quantitative β-hCG monitoring may assist when ultrasound findings are indeterminate.
Correlate with clinical symptoms (bleeding, pain) and prior imaging.
Differential diagnosis
Normal very early intrauterine pregnancy (too early to visualize embryo).
Decidualized endometrium / pseudosac (in ectopic pregnancy).
Subchorionic hemorrhage with collapsed sac.
Anembryonic pregnancy (blighted ovum).
Partial molar pregnancy (when cystic placental changes present).
Teaching points
Empty sac sign alone in very early pregnancy is not diagnostic—use MSD thresholds and repeat scans.
MSD ≥ 25 mm with no embryo/yolk sac on high-quality TVS historically supports diagnosis of anembryonic pregnancy.
CRL ≥ 7 mm without cardiac activity indicates embryonic demise (separate but related diagnostic rule).
Always integrate with serial β-hCG and clinical picture before definitive management.
References
Society of Radiologists in Ultrasound (SRU) consensus guidelines on early pregnancy — follow diagnostic cutoffs.
AIUM Practice Parameter for the Performance of Obstetric Ultrasound Examinations.
Discussion
The empty sac sign often presents a diagnostic dilemma when a patient presents early. Imaging technique (transvaginal vs transabdominal), operator experience, and machine resolution all influence detection thresholds. Recent guideline updates emphasize conservative repeat scanning timelines to avoid false-positive diagnosis of embryonic demise.
Empty Sac Sign — single conclusion (entities fixed)
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