A 27-year-old primigravida presents at 31 weeks with sudden painless vaginal bleeding immediately after spontaneous rupture of membranes, followed by fetal bradycardia. Which investigation will confirm the underlying cause?
- A Speculum examination to visualise the cervix
- B Kleihauer-Betke test on maternal blood
- C Transvaginal colour Doppler showing fetal vessels crossing the internal os ✓
- D CTG with vibroacoustic stimulation
Correct answer: C. Transvaginal colour Doppler showing fetal vessels crossing the internal os
Explanation
Painless bleeding at membrane rupture with acute bradycardia is the classic presentation of vasa previa, where unprotected velamentous vessels lie over the internal os. Transvaginal ultrasound with colour Doppler demonstrating fetal vessels across the os is diagnostic. The Kleihauer test detects fetomaternal haemorrhage but cannot localise the source, and speculum examination risks tearing the vessels.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.