In the management of vasa praevia, which specific Doppler finding on second-trimester ultrasound most reliably identifies the condition?

• A Absent end-diastolic flow in the umbilical artery
• B Colour Doppler demonstrating fetal vessels crossing the internal os with waveform showing umbilical artery pulsatility ✓
• C Reversed 'a' wave in the ductus venosus
• D Increased pulsatility index in uterine artery

Explanation

Vasa praevia is defined as fetal blood vessels running in the fetal membranes (velamentous cord insertion or succenturiate lobe vessels) that cross or lie within 2 cm of the internal cervical os, unsupported by placental tissue. On transvaginal colour Doppler, vessels traversing the internal os show arterial or venous waveforms consistent with fetal circulation (umbilical artery or vein pulsatility). This is the gold standard prenatal diagnosis. Absent end-diastolic flow is a sign of fetal compromise from placental insufficiency. Reversed ductus venosus 'a' wave reflects right heart pressure. Uterine artery PI elevation is a preeclampsia/IUGR marker.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.