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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Vasa praevia

Obstetrics and gynaecology · UK scope · Sources checked 7 Sept 2026 · Clinical review pending

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Membrane rupture with bleeding and fetal bradycardia

Torn vessels in vasa praevia can cause rapid fetal blood loss while maternal observations remain normal.

Action: Call an immediate obstetric and neonatal emergency, expedite caesarean birth when the fetus is potentially viable and vaginal birth is not already imminent, and prepare neonatal resuscitation with urgent blood replacement.

Overview

Recognise unprotected fetal vessels near the cervix, prevent rupture through antenatal planning, and respond immediately to bleeding accompanied by acute fetal compromise.

The danger in vasa praevia comes from whose blood is lost. The affected vessels belong to the fetus and lack the normal protection of placental tissue or the umbilical cord's Wharton's jelly. A vessel stretched across the lower membranes may rupture as the cervix opens or membranes break. Even a volume that would be modest for an adult can be critical for a small fetus. Maternal pulse and blood pressure can therefore remain reassuring while fetal oxygen delivery collapses. Compression without obvious rupture may also impair fetal circulation.

Anatomical risk clues include a velamentous cord insertion, an accessory or bilobed placenta, and present or earlier low placentation. Assisted conception increases the likelihood of relevant placental abnormalities. Targeted assessment should map the cord insertion, placental lobes and any connecting vessels when risk is identified. A label of resolved low-lying placenta does not by itself establish that the lower membranes are clear of vessels. Conversely, apparent vessels on a single scan need expert confirmation because maternal veins and a mobile cord loop can mimic the finding.

Aetiology

01

Velamentous insertion

The cord inserts into the membranes rather than directly into the placental disc, leaving a segment of fetal vessels exposed before they reach placental tissue.

02

Separated placental lobes

Vessels connecting an accessory lobe or the portions of a bilobed placenta may pass through membranes across the lower uterine segment near the cervical opening.

Pathophysiology

  1. 1
    Loss of vessel protection

    Membranous vessels lack the cushioning of Wharton's jelly or surrounding placental tissue, making them vulnerable to compression and mechanical tearing during labour.

  2. 2
    Rupture at membrane opening

    Spontaneous membrane rupture or an amniotomy can tear an exposed vessel, allowing fetal blood to escape before birth and rapidly reducing circulating volume.

  3. 3
    Fetal circulatory collapse

    Blood loss lowers fetal preload and oxygen-carrying capacity, producing bradycardia and shock while maternal circulation may remain unaffected because the bleeding is fetal.

Clinical features and red flags

Antenatal vessel finding

A vessel traversing the lower membranes on imaging requires assessment of its course and whether Doppler confirms a fetal arterial or venous origin.

Bleeding after rupture

Sudden vaginal bleeding at membrane rupture accompanied by fetal deterioration is a classic warning of torn fetal vessels.

Stable mother, compromised fetus

Normal maternal physiology must not reassure the team when the fetus may be losing blood into the amniotic cavity or vagina.

High-risk placental anatomy

An accessory lobe, bilobed placenta or velamentous insertion creates a reason to inspect the vessels near the cervix carefully.

Red flags requiring action

  • Vaginal bleeding immediately after spontaneous or artificial membrane rupture with fetal bradycardia requires emergency action for possible fetal vessel rupture.
  • Known vasa praevia with labour, ruptured membranes or new bleeding needs immediate hospital assessment and a senior delivery decision.

Investigations

  1. 01
    Targeted transvaginal colour Doppler ultrasoundFirst step
    Why
    Map suspected vessels in relation to the internal os and lower membranes.
    Interpretation and limitations
    Expert technique is needed to avoid both missed vessels and false-positive maternal vascular structures; add pulsed Doppler where necessary to establish fetal origin.
  2. 02
    Placental and cord-insertion mapping
    Why
    Identify velamentous insertion and vessels linking a main placenta to an accessory lobe.
    Interpretation and limitations
    Document the entire relevant vessel course rather than relying only on the distance of the nearest placental edge from the cervix.
  3. 03
    Third-trimester confirmation scan
    Why
    Establish whether the antenatal finding persists before finalising premature caesarean birth.
    Interpretation and limitations
    Resolution can occur, so reassessment reduces unnecessary intervention; uncertainty requires specialist review rather than assuming a negative outcome.
  4. 04
    Immediate fetal heart assessment during symptoms
    Why
    Detect bradycardia or other compromise from vessel compression or blood loss.
    Interpretation and limitations
    Acute compromise with bleeding dictates urgent management; a laboratory test for fetal blood must not delay necessary birth.
  5. 05

Differential diagnosis

01

Maternal placental bleeding

Praevia or abruption can also cause bleeding and fetal compromise; emergency assessment must address maternal haemorrhage while considering the possibility of fetal blood loss.

02

Cord prolapse or compression

Abrupt bradycardia after membrane rupture may result from cord obstruction rather than haemorrhage, but both conditions demand immediate assessment and expedited delivery when unresolved.

03

Maternal vessels on Doppler

Prominent cervical or uterine vessels may mimic vasa praevia on colour imaging; tracing their course and assessing Doppler characteristics helps establish their origin.

Management

01DetectionConfirm anatomy and explain the riskFirst stepA screening or targeted scan identifies possible vessels near the cervix.+
  1. 1Refer for expert ultrasound with colour and pulsed Doppler to distinguish vasa praevia from maternal vessels or a transient cord loop.
  2. 2Record placental lobes, insertion type and the course of relevant vessels, then arrange third-trimester confirmation of persistence.
  3. 3Explain the difference between maternal bleeding and fetal vessel rupture, and give a clear instruction to contact maternity services immediately for symptoms.
02PreventionPrepare birth before labour or membrane ruptureVasa praevia is confirmed and the patient remains clinically stable.+
  1. 1Agree the place of care individually, considering admission from 30–32 weeks when bleeding, preterm-labour risk or access to emergency care makes it appropriate.

Complications

01

Fetal exsanguination

Rupture can cause life-threatening anaemia and hypovolaemia within a short interval, requiring urgent birth and neonatal resuscitation with blood-product support.

02

Hypoxic neurological injury

Prolonged circulatory compromise can injure the fetal brain even when emergency delivery restores circulation, necessitating specialist neonatal assessment and follow-up.

03

Iatrogenic prematurity

Planned birth before spontaneous labour reduces rupture risk but creates respiratory, feeding and temperature-control burdens that must be weighed during antenatal planning.

Monitoring and follow-up

  • At every planned contact review bleeding, uterine activity and fluid loss, and confirm the patient knows the fastest route to a unit able to perform emergency caesarean birth.
  • Repeat relevant ultrasound in the third trimester to confirm persistence and update the documented placental and vessel map before surgery.
  • For inpatient care individualise observation and VTE prevention to bleeding risk, mobility and obstetric assessment; admission alone cannot prevent vessel rupture.
  • After birth follow neonatal haemoglobin, perfusion and neurological status when haemorrhage was suspected, with the neonatal team deciding further investigation.
  • Provide postnatal review that explains diagnostic certainty, how the birth plan was chosen and what early placental assessment may be useful in another pregnancy.

Special situations

The volume belongs to a fetus

A small pool of blood can represent a large fraction of fetal circulating volume, so adult visual estimates are an unsafe way to judge risk.

Resolved placenta does not clear vessels

Placental tissue and exposed vessels do not necessarily change position identically, making targeted vessel assessment important when earlier low implantation was recorded.

Published and draft guidance differ

A peer-review draft may propose a different planned-birth interval, but its provisional recommendation should not be presented as the issued national standard.

Screening and diagnostic assessment differ

Recognising risk and arranging targeted expert imaging does not imply that universal population screening for every pregnancy is an established UK programme.

Common pitfalls

  1. 01

    Waiting for maternal hypotension before accepting that a bleeding episode may threaten fetal survival.

  2. 02

    Performing amniotomy when known or suspected vessels cross the lower membranes.

  3. 03

    Cancelling specialist follow-up solely because the placental edge has moved away from the cervix.

  4. 04

    Using a test to identify fetal haemoglobin as a reason to defer emergency delivery during persistent fetal bradycardia.

Practice

Two practice questions

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Question 1 of 2
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Obstetrics and gynaecologyOriginal SBA

Bleeding with a stable mother

Immediately after membrane rupture at 35 weeks, a patient with no prior uterine surgery loses a modest amount of painless vaginal blood and the fetal heart rate falls persistently to 70 beats/minute. The uterus is nontender and maternal observations remain normal. Which explanation is most strongly suggested?

Choose one answer, then submit
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Sources and review status5 sources · checked 7 Sept 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 7 Sept 2026; clinical approval remains outstanding.

  • RCOG Green-top 27b vasa praevia published guideline
  • RCOG vasa praevia guideline status and summary
  • NICE recommendations for preterm labour and birth
  • RCOG patient information on low placentation and fetal vessels
  • RCOG Green-top 74 antenatal corticosteroid regimens

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
Antenatal diagnosis changes management profoundly: the aim is birth before labour or membrane rupture, with enough gestation gained to reduce neonatal prematurity. Published RCOG Green-top 27b recommends individualised consideration of admission from 30–32 weeks and regards planned caesarean birth at 34–36 weeks as reasonable in asymptomatic cases. These are not automatic dates for every patient. Bleeding, contractions, multiple pregnancy, cervical changes and distance from a suitable unit affect the plan. The 2026 peer-review draft is not a replacement for the currently published guideline; local specialist teams may discuss emerging evidence while stating the basis of their recommendations.

During an acute presentation the familiar diagnostic triad may be incomplete. Membranes may have ruptured without a clear history, external loss may be small, and bradycardia may be the first recognised sign. Call the neonatal team explicitly about suspected fetal haemorrhage so compatible emergency blood can be available. Tests intended to distinguish fetal from maternal blood are too slow to determine emergency care when fetal wellbeing is threatened. After birth, inspect the placenta and membranes, record findings and provide an explanation to the family.

Key points

  • Vasa praevia means fetal vessels run unprotected in membranes near or across the cervical opening.
  • Type I is associated with velamentous cord insertion; type II connects placental lobes through exposed membranous vessels.
  • A low placenta that later appears to resolve can coexist with persistent vessels near the cervix.
  • Targeted transvaginal ultrasound with colour and pulsed Doppler distinguishes fetal vessels from maternal vascular structures.
  • Confirm persistence during the third trimester because a second-trimester finding may resolve as anatomy changes.
  • The published RCOG 27b pathway considers planned caesarean birth at 34–36 weeks reasonable, with individual assessment of admission and prematurity risk.
  • Do not delay emergency birth for an Apt test, a repeat scan or laboratory proof that bleeding is fetal.
Neonatal haemoglobin and perfusion assessment
Why
Measure blood-loss consequences and guide resuscitation after suspected vessel rupture.
Interpretation and limitations
Clinical shock and anaemia require neonatal-led urgent replacement; testing should run alongside resuscitation and not become a prerequisite for treatment.
2
Plan caesarean birth within the published 34–36-week range, adjusting for the individual balance of rupture risk and prematurity with fetal-medicine and neonatal input.
  • 3Time corticosteroids to likely preterm birth under the current corticosteroid pathway and record a contingency plan for labour or membrane rupture before the booked date.
    • 03EmergencyRespond to suspected fetal vessel ruptureBleeding follows membrane rupture or known vasa praevia develops labour with fetal danger.+
    1. 1Declare the suspected fetal haemorrhage clearly, call senior obstetric and neonatal teams, and organise immediate operative delivery where indicated.
    2. 2Do not wait for laboratory differentiation of fetal blood, repeated sonography or completion of antenatal medicines before a time-critical birth.
    3. 3Ensure neonatal resuscitation and emergency transfusion capability are ready, then document placental findings and arrange a family debrief after stabilisation.
    Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
    Helps reduce neonatal respiratory and other prematurity-related complications before planned early birth.

    Betamethasone for anticipated preterm caesarean birth

    The betamethasone sodium phosphate/acetate regimen is 12 mg intramuscularly repeated after 24 hours. Confirm the approved local schedule for phosphate-only preparations and coordinate treatment with likely birth.

    Diabetes requires enhanced glycaemic planning, late-preterm treatment needs an individual benefit-harm discussion, and suspected vessel rupture takes priority over steroid completion.

    Restores the infant's circulating red-cell volume after acute fetal blood loss.

    Neonatal emergency red-cell replacement

    Suspected neonatal haemorrhagic shock requires the neonatal resuscitation team's weight-based emergency transfusion prescription and compatible emergency blood; volume, rate and reassessment are determined immediately from perfusion, gestation and response.

    This is a neonatal rather than maternal prescription. Alert the transfusion laboratory early and do not substitute maternal crystalloid resuscitation for treatment of fetal exsanguination.