A 26-year-old with 5 weeks amenorrhoea and beta-hCG of 1,600 mIU/mL undergoes transvaginal ultrasound. A fluid collection is seen lying centrally within the endometrial cavity, elongated in shape, containing no yolk sac or fetal pole, with a single echogenic rim. Which finding would most reliably confirm a true early intrauterine gestation rather than this collection?

• A Increase in size of the collection on repeat scan
• B Presence of a double decidual sac sign with an eccentric sac containing a yolk sac ✓
• C Movement of the collection with probe pressure
• D Rising beta-hCG above the discriminatory zone

Explanation

The described collection is a pseudogestational sac, a decidual reaction to ectopic-produced hormones. It lies centrally in the cavity, lacks a yolk sac or fetal pole, and shows only a single rim. A true gestational sac is eccentrically placed within decidua and demonstrates the double decidual sac sign, produced by the inner decidua capsularis and outer decidua vera. Rising hCG merely confirms ongoing trophoblast activity anywhere, including an ectopic site, so it cannot localise the pregnancy.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.