Vasa previa
Summary
Fetal umbilical vessels run through the membranes over or near the internal cervical os, unprotected by cord or placenta. Rupture of membranes can lacerate these vessels and cause rapid, often fatal fetal exsanguination.
Detail
Classic risk factors include velamentous cord insertion (cord inserts into membranes rather than placental disc), succenturiate/bilobed placenta, low-lying placenta or placenta previa, and IVF pregnancies. Diagnosis is by transvaginal ultrasound with color Doppler showing fetal vessels crossing the os; antenatal detection is critical because undiagnosed vasa previa carries very high perinatal mortality. Classic presentation: painless vaginal bleeding immediately after rupture of membranes accompanied by fetal bradycardia or sinusoidal heart-rate tracing (fetal anemia). Management is scheduled cesarean delivery at ~34-37 weeks before labor or membrane rupture. Contrast with placenta previa (painless maternal bleeding) and abruption (painful bleeding with hypertonic uterus).
Sources
- First Aid for USMLE Step 2 CK
- Williams Obstetrics
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