Vasa Praevia

Vasa praevia is a condition in which fetal vessels run through the membranes, unprotected by the umbilical cord or placental tissue. They lie across or within 2 cm of the internal cervical os, ahead of the presenting part. Incidence is about 1 in 2,500 pregnancies.

Untreated, the vessels can rupture with the membranes, causing fetal exsanguination in minutes. Perinatal mortality in undiagnosed cases approaches 50 to 60%. With antenatal diagnosis and planned caesarean, survival exceeds 95%.

• Type I is associated with velamentous cord insertion.
• Type II is associated with a bilobed or succenturiate lobed placenta, with the vessels connecting the lobes.

Risk factors:

• Low lying placenta or placenta praevia in the second trimester (that appears to migrate).
• In vitro fertilisation (up to 10-fold increased risk).
• Multiple pregnancy.
• Velamentous cord insertion.
• Bilobed or succenturiate placenta.

• Painless vaginal bleeding at rupture of membranes (spontaneous or artificial) with fetal bradycardia, a sinusoidal pattern on cardiotocography, and rapid fetal deterioration (Benckiser haemorrhage)
• Palpable pulsating vessels on vaginal examination (rarely identified)
• Most cases are asymptomatic antenatally, so ultrasound is essential
• Fetal anaemia and fetal death if unrecognised

• Transvaginal ultrasound with colour and pulsed Doppler (the gold standard): parallel or linear echolucent tubular structures crossing the internal os with fetal heart rate velocity waveform on pulsed Doppler; the vessels do not move with maternal position change
• Screening: second trimester anatomy scan with cord insertion and placental location, with transvaginal assessment of all women with risk factors (low lying placenta, IVF, velamentous insertion, succenturiate lobe) at 18 to 24 weeks
• Differentiate from a funic presentation (cord moves with position change)
• MRI if ultrasound uncertain
• Apt test or alkali denaturation test on vaginal blood to detect fetal haemoglobin (not time feasible in an emergency)

• Antenatal: corticosteroids for fetal lung maturity at 28 to 32 weeks (betamethasone 12 mg IM, two doses 24 hours apart).
• Surveillance, outpatient or inpatient, from 30 to 32 weeks. Consider hospitalisation with symptoms, short cervix, contractions, or risk of rapid transport.
• Avoid sexual intercourse and digital cervical examination. Use cervical length surveillance, non-stress tests and ultrasound for growth.
• Delivery: planned caesarean section at 34 to 36 weeks 6 days (commonly 35 to 36 weeks), before labour or rupture of membranes, in a centre with neonatal intensive care and blood bank support.
• Emergency: for labour, bleeding or membrane rupture, immediate category 1 caesarean delivery. The neonatal resuscitation team should be prepared for transfusion of O-negative blood (10 to 20 mL/kg). Manage the neonate for hypovolaemic shock and anaemia.
• Intraoperative: avoid rupture of membranes near the vessels, with an incision away from the vessels.