PassFinals
Obstetrics

Vasa praevia

Unprotected fetal vessels run through the membranes over or close to the internal cervical os; if the membranes rupture, the vessels can tear and cause rapid fetal exsanguination.

In a nutshell

Vasa praevia is unprotected fetal vessels running through the membranes over or close to the internal os. Membrane rupture can tear the vessels and cause rapid fetal exsanguination. Targeted transvaginal colour Doppler and planned prelabour caesarean birth prevent the catastrophic presentation; bleeding with fetal compromise after rupture is an immediate emergency.

Classic presentation

Painless bleeding immediately after rupture of membranes followed by fetal bradycardia or another acute CTG abnormality, with little maternal blood loss and a risk factor such as velamentous cord insertion or an accessory placental lobe.

Key points

  • The bleeding is fetal, so maternal observations may initially be normal.
  • Think of vasa praevia when painless bleeding follows rupture of membranes and the fetal heart rate deteriorates.
  • Risk associations include velamentous insertion, bilobed or succenturiate placenta, low-lying placenta, IVF and multiple pregnancy.
  • Use specialist transvaginal colour Doppler to define fetal vessels near the internal os.
  • Plan caesarean birth before labour or membrane rupture at an individualised gestation.
  • Do not delay emergency birth for confirmatory imaging when fetal compromise is present.

First-line investigation

In an at-risk pregnancy, specialist transvaginal ultrasound with colour Doppler; in acute bleeding after rupture, continuous CTG and immediate senior assessment while preparing emergency birth.

Management

Recognise the fetal emergency

  • After rupture of membranes with bleeding and fetal compromise, call senior obstetric, anaesthetic and neonatal teams, start continuous CTG and expedite emergency caesarean birth without waiting for imaging.1,3

Assess blood loss and prepare neonatal support

  • Assess the mother using ABCDE and prepare blood support as indicated, while anticipating neonatal resuscitation, anaemia assessment and transfusion after suspected fetal blood loss.1,4

Prepare for preterm birth

  • Use NICE NG25 to guide antenatal corticosteroid decisions when preterm birth is anticipated, following current prescribing and local protocol; never delay emergency birth for steroids.5,6

Prevent membrane rupture in confirmed disease

  • Arrange an individualised specialist plan and prelabour caesarean birth before spontaneous or planned membrane rupture, with clear advice to attend urgently for bleeding, contractions or suspected rupture.1

Exam traps

  • A small volume of vaginal blood can represent life-threatening fetal haemorrhage.
  • Vasa praevia is usually painless, unlike abruption.
  • Avoid artificial rupture of membranes when vasa praevia has not been excluded in a high-risk situation.
  • Antenatal diagnosis is the prevention strategy; emergency caesarean after rupture may be too late.
  • A planned delivery date must be individualised; do not substitute an unsupported universal gestational threshold.

Illustrations

Colour Doppler of a fetal vessel near the cervixTransvaginal colour Doppler showing fetal blood flow close to the internal cervical os, the key antenatal finding in vasa praevia.Thanasa E et al., Cureus 2024, CC-BY-4.0 · CC-BY-4.0

Key sources

  1. RCOG Green-top Guideline No. 27b, Vasa Praevia: Diagnosis and Management (Current published UK vasa praevia guidance: diagnosis, risk associations and planned or emergency management)Updated 27 Sept 2018
  2. RCOG Green-top Guideline No. 27a, Placenta Praevia and Placenta Accreta Spectrum (Current RCOG specialist placenta guidance reviewed 30 June 2026, used for placental and cord-risk context)Updated 30 Jun 2026
  3. NICE NG121, Intrapartum care for women with obstetric complications (Current NICE recommendations for intrapartum bleeding, maternal and fetal assessment, blood testing and multidisciplinary escalation)
  4. RCOG Green-top Guideline No. 47, Blood Transfusions in Obstetrics (UK obstetric transfusion guidance for major haemorrhage and blood-product support)Updated 29 May 2015
  5. NICE NG25, Preterm labour and birth (Current NICE recommendations last updated 10 June 2022 for antenatal corticosteroids when preterm birth is suspected, established or planned)Updated 10 Jun 2022
  6. BNF, current obstetric prescribing information (UK prescribing source for antenatal corticosteroids and emergency obstetric medicines; direct access was restricted and unsupported doses were omitted)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.