Conditions · Obstetrics and gynecology
Vasa previa !
Unprotected baby blood vessels run across the membranes over the cervix. If they tear when the waters break, the baby can bleed to death within minutes.
Updated 2026-11-01
Structures involved
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Why it happens
What it is
A condition in which fetal blood vessels, unprotected by umbilical cord or placental tissue, run through the membranes over or very close (within about 2 cm) to the internal cervical os. When the membranes rupture or the cervix dilates, these vessels can tear and the bleeding is fetal blood.
Who gets it
Uncommon: about 1 in 1,200 to 1 in 2,500 deliveries, and much more frequent after in vitro fertilisation. Without prenatal diagnosis fetal mortality may reach about 60%; with prenatal diagnosis and planned caesarean delivery, most babies survive. Many units in Latin America now look for cord insertion on routine anatomy ultrasound.
Causes
- Velamentous cord insertion: the cord inserts into the membranes and the vessels travel unprotected to the placenta (type I)
- Bilobed or succenturiate-lobe placenta with connecting vessels crossing the cervix (type II)
- Vessels running over the cervix after a low-lying placenta migrates upward
Risk factors
- Velamentous cord insertion
- Bilobed, multilobed or succenturiate placenta
- Low-lying placenta or placenta previa in the second trimester
- In vitro fertilisation
- Multiple pregnancy
- Previous uterine surgery or caesarean delivery
Pathophysiology
The vessels in the membranes lack the protective Wharton jelly of the cord. When the membranes rupture, spontaneously or artificially, or are stretched during labour, a vessel can tear. The fetus has a small total blood volume, so even a modest loss causes rapid fetal anaemia, bradycardia and death. The vessels can also be compressed by the presenting part, causing fetal hypoxia without bleeding.
Classification
- Type I: associated with velamentous cord insertion
- Type II: vessels between lobes of a bilobed or succenturiate placenta
Symptoms and signs
- Usually no symptoms before rupture (found on ultrasound)
- Painless vaginal bleeding at or just after rupture of the membranes
- Fetal heart rate changes: sudden bradycardia or a sinusoidal pattern
- The mother is haemodynamically stable because the blood lost is fetal
Diagnosis
- Clinical
- Ideally diagnosed before labour on ultrasound. In labour, suspect it when painless bleeding appears at membrane rupture with sudden fetal distress while the mother remains stable.
- Tests
- Tests for fetal haemoglobin in the vaginal blood exist, but in an emergency delivery must not wait for them. Neonatal haemoglobin after birth to guide transfusion.
- Imaging
- Transvaginal ultrasound with colour Doppler showing fixed fetal vessels running over or near the internal os, with fetal (umbilical arterial) waveform; the vessels do not move with position change, unlike a funic presentation. Cord insertion should be checked in the mid-trimester scan.
Differential diagnosis
- Placenta previa
- Placental abruption
- Cervical bleeding or bloody show
- Funic (cord) presentation
- Uterine rupture
Goal of treatment
Deliver the baby by caesarean section before the membranes rupture, balancing the risks of prematurity against the risk of vessel rupture, and act within minutes if bleeding occurs.
Treatment
- Follow-up
- After prenatal diagnosis: fetal surveillance from the third trimester, education about warning signs, and often hospital admission around 30–34 weeks for close observation.
- Medical
- Antenatal corticosteroids for fetal lung maturity before planned preterm delivery or if bleeding occurs.
- Surgical
- Planned caesarean delivery before labour, usually around 34–37 weeks; emergency caesarean if the membranes rupture, bleeding occurs or the fetal heart rate is non-reassuring.
- Acute
- Neonatal team present at delivery, ready for resuscitation and blood transfusion of the newborn.
Complications
- Fetal exsanguination and death
- Fetal hypoxia from compression of the vessels
- Neonatal anaemia needing transfusion
- Complications of preterm birth
Prognosis
Excellent for the baby when diagnosed before labour and delivered by planned caesarean; very poor when first recognised at membrane rupture. The mother is rarely in danger.
Prevention
- Not preventable, but deaths are preventable by prenatal detection: documenting cord insertion at the anatomy scan and targeted transvaginal Doppler in women with risk factors
- Avoid artificial rupture of membranes when vessels over the cervix are suspected
Test yourself
Think of the answer, then tap the question to see it.
What is the classic triad of ruptured vasa previa?
Painless vaginal bleeding at rupture of membranes, followed by fetal bradycardia, with a stable mother.
Whose blood is lost in vasa previa?
The fetus’s: that is why the baby deteriorates rapidly while the mother stays stable.
Which placental cord anomaly is most associated with vasa previa?
Velamentous cord insertion.
What is the recommended delivery plan when vasa previa is diagnosed before labour?
Planned caesarean delivery before labour, usually around 34–37 weeks, after antenatal corticosteroids.
Related conditions
- Placenta praevia
- Placental abruption
- Premature rupture of membranes (PROM and PPROM)
- Intrapartum fetal compromise (non-reassuring fetal status)
- Stillbirth (intrauterine fetal death)
- Preterm labour and birth
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Vasa Previa (Merck Manual Professional Edition, 2024); Vasa Previa (Cleveland Clinic, 2024).
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