Vasa Previa on Ultrasound

Vasa previa occurs when unprotected fetal vessels cross the internal cervical os, either within the membranes or via a low-tethered umbilical cord.

Prenatal diagnosis relies on the transvaginal ultrasound approach.

1. Color Doppler: Use to visualize vessels directly overlying the cervix.

2. Pulsed Doppler**: Essential to confirm the vascular flow is fetal in origin (differentiating it from maternal vessels). ​Because these vessels lack protection from placental tissue, they are at high risk of rupture during labor or membrane rupture, leading to rapid fetal exsanguination.