Vasa previa is most reliably diagnosed by which investigation, and what is the risk to the fetus if it is undiagnosed?

• A MRI pelvis; risk of placental abruption
• B Abdominal CTG; risk of cord prolapse
• C Amniocentesis at 28 weeks; risk of preterm delivery
• D Transvaginal color Doppler ultrasound showing fetal vessels crossing the internal os; risk of catastrophic fetal hemorrhage and death (60–75% perinatal mortality if undiagnosed at membrane rupture) ✓

Explanation

Vasa previa is diagnosed by transvaginal color Doppler ultrasound demonstrating fetal vessels traversing the membranes overlying the internal cervical os. At membrane rupture, these vessels are torn causing fetal exsanguination — perinatal mortality is 50–75% when undiagnosed. When diagnosed antenatally, elective cesarean at 34–36 weeks reduces mortality to <5%. Risk factors include velamentous cord insertion, bilobed/succenturiate placenta, and IVF pregnancy.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.