AKT · Obstetrics & gynaecology/Late pregnancy & labourlow yield

Vasa praevia

Fetal vessels crossing the os (unsupported)

Overview

Unprotected fetal blood vessels (from a velamentous cord insertion or succenturiate lobe) running through the membranes over the cervical os. When the membranes rupture, the vessels tear — causing PAINLESS bleeding of FETAL blood with rapid fetal exsanguination.

Recognise

Painless vaginal bleeding occurring AT rupture of membranes
Acute, severe FETAL distress/bradycardia (the blood is fetal, not maternal)
Mother remains haemodynamically stable

Red flags

Fetal exsanguination is rapid — minutes matter; emergency caesarean

Differentials & how to tell them apart

Placenta praeviamaternal bleeding, no specific link to ROM, maternal not fetal compromise

Placental abruptionPAINFUL, tender uterus, maternal bleeding

Maternal bleeding causesmother becomes shocked; in vasa praevia the FETUS deteriorates while mother is stable

Investigations

Ideally detected antenatally on USS (transvaginal colour Doppler) — antenatal diagnosis allows planned caesarean. Acute: the triad of ROM + painless bleeding + fetal bradycardia.

Management

Immediate emergency caesarean section

1Antenatal diagnosis: plan elective caesarean (~34–36 weeks) with steroids before labour/ROM.Gate: Bleeding at ROM with acute fetal distress but a STABLE mother → emergency caesarean immediately (fetal blood loss)
2Neonatal resuscitation including transfusion for fetal anaemia.

Emergency caesarean section — immediate — fetal survival depends on speed

Neonatal resuscitation/transfusion — fetal blood loss

Key points

The discriminator: the FETUS crashes while the MOTHER stays well — because the blood being lost is fetal. Antenatal detection is the only way to reliably save the baby.

Monitor & prognosis

Fetal status; neonatal Hb after delivery.

Excellent if diagnosed antenatally and delivered by planned caesarean; high fetal mortality if it ruptures undiagnosed.

Source: RCOG Green-top 27b