Velamentous cord insertion with vasa praevia most commonly occurs in which placental configuration and why does it carry a particularly high fetal mortality risk?
- A Bipartite placenta; because fetal vessels are unprotected by Wharton's jelly and cross the internal os ✓
- B Succenturiate lobe; because vessel compression causes umbilical cord prolapse
- C Circumvallate placenta; because the extrachorial membrane traps fetal vessels
- D Accessory lobe in the lower segment; because vessel rupture at membrane rupture causes rapid maternal exsanguination
Correct answer: A. Bipartite placenta; because fetal vessels are unprotected by Wharton's jelly and cross the internal os
Explanation
Vasa praevia most commonly occurs with velamentous cord insertion (vessels course through the membranes without Wharton's jelly protection) and with accessory/succenturiate lobes where fetal vessels must traverse between lobes. In Type I vasa praevia, the vessels overlie the internal cervical os. When membranes rupture — spontaneously or artificially — these unprotected fetal vessels tear, causing immediate fetal haemorrhage with 75–95% fetal mortality if undiagnosed. The fetus (with ~250 mL total blood volume at term) cannot tolerate even small blood losses.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.