Vasa Previa

Summary

Vasa previa is a rare condition where fetal vessels cross the cervical os, risking rupture and fetal death; diagnosis is by Doppler ultrasound, and urgent cesarean delivery is required.

Definition

 Vasa previa is a rare but life-threatening obstetric condition in which unprotected fetal vessels traverse the fetal membranes across or near the internal cervical os, placing them at risk of rupture during labor or membrane rupture. It is the only cause of antepartum hemorrhage of purely fetal origin. The estimated incidence is approximately 1 in 2,500 births.

Etiology and Pathophysiology

Vasa previa typically arises from placental or cord abnormalities, most commonly:

• Velamentous insertion of the umbilical cord (vessels insert into the membranes instead of the placental disk).

• Succenturiate or bilobate placenta, where connecting vessels run through the membranes between lobes.

These unsupported vessels are highly vulnerable to rupture with membrane rupture or cervical dilatation. As the bleeding originates from the fetoplacental circulation, even a small volume of blood loss can rapidly lead to fetal exsanguination and death.

Risk Factors

• Placental anomalies (velamentous insertion, succenturiate/bilobate placenta)

• Placenta previa or low-lying placenta

• In vitro fertilization

• Multiparity

• Advanced maternal age

Clinical Features

The classic presentation is the triad of:

• Painless vaginal bleeding after rupture of membranes (fetal blood loss)

• Acute fetal distress (bradycardia, decelerations, sinusoidal fetal heart tracing)

• Rapid progression to fetal compromise or death if unrecognized

In about 25% of cases, bleeding can occur even without rupture of membranes due to vessel compression.

Diagnosis

Although often diagnosed postpartum on examination of the placenta and membranes, antenatal suspicion is crucial.

• Ultrasound with color Doppler (transvaginal or transabdominal) can demonstrate fetal vessels coursing across the internal os with altered blood flow.

• Prenatal diagnosis markedly improves perinatal outcomes.

Management

• Emergency cesarean delivery is required once vasa previa is diagnosed in labor or with rupture of membranes, as fetal survival depends on immediate intervention.

• In pregnancies diagnosed antenatally, planned cesarean delivery before the onset of labor or rupture of membranes (typically 34–37 weeks) is recommended to prevent catastrophic fetal hemorrhage.