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Vasa praevia

Vasa praevia is rare in pregnancy but it can cause complications. We discuss what it is, risk factors, symptoms and its management during labour.  

Vasa praevia (also called vasa previa) affects between one in 2,000 and one in 6,000 pregnancies (RCOG, 2011). In most pregnancies, blood vessels from the umbilical cord insert directly into the placenta. With vasa praevia the baby’s blood vessels run through the membranes covering the cervix (NHS Choices, 2018).   

What is vasa praevia?

  • Vasa praevia is where one or more of the baby’s placental or umbilical blood vessels cross the entrance to the birth canal under the baby.
  • Having vasa praevia increases the chance that if the membranes tear during labour (naturally or by a health professional), the blood vessels might also tear. This would result in the baby potentially losing a life-threatening amount of blood.
  • It is also possible that when the baby drops into the pelvis, the vessels may be compressed, affecting its blood supply and causing oxygen deprivation. 

    (RCOG, 2011; Vasa Praevia, 2018)

Risk factors for vasa previa

Vasa praevia is more likely if you have one of the following:

  • IVF pregnancy
  • low-lying placenta (placenta praevia)
  • bilobed placenta, which is where the placenta has more than one part
  • velamentous cord insertion (VCI), which is where the cord inserts into the membranes and travels within the membranes before joining the placenta (the cord should insert straight into the placenta)
  • multiple pregnancy. 

    (RCOG, 2011; UK NSC, 2017a)

If you had vasa praevia in a previous pregnancy, you have the same risk as anyone of having it in your next pregnancy. That is, if you don’t have the original risk factors (RCOG, 2011; UK NSC, 2017a).

Antenatal prevention and treatment of anaemia is recommended to help avoid vasa previa.


  • Women may have a sudden onset of painless vaginal bleeding in the second or third trimester of pregnancy.
  • Some women might not have symptoms.

    (Vasa Praevia, 2018)


Vasa praevia may be diagnosed by fresh vaginal bleeding when the membranes rupture, along with changes in the baby’s heart rate (RCOG, 2011). While this can be very dangerous for the baby, antenatal diagnosis of vasa praevia improves outcomes.

If bleeding happens when the membranes rupture and the baby is not coping, immediate birth by caesarean will be recommended (RCOG, 2011).

"While vasa praevia can be seen on ultrasound, screening everyone for it is not accurate enough." 

Management during labour

If you have vasa praevia confirmed in your third trimester, it’ll be recommended you have a caesarean birth (RCOG, 2011). You might be invited to stay on the antenatal ward, so that you are nearer to surgical and neonatal support (RCOG, 2011).


Vasa praevia can be detected by ultrasound. Universal screening is not recommended because nobody knows how many babies are affected and the test is not reliable enough (UK NSC, 2017b)

The screening test might also pick up other conditions, like velamentous cord insertion (VCI), that have unknown implications and no agreement on how to manage them (UK NSC, 2017b). That means screening could lead to a large number of pregnancies being considered to be at risk. This in turn could result in significant anxiety and potentially a large number of unnecessary early caesarean births.

If you’re concerned about any symptoms you have in your pregnancy talk to your midwife, health visitor or GP.

This page was last reviewed in January 2018.

Further information

Our support line offers practical and emotional support with feeding your baby and general enquiries for parents, members and volunteers: 0300 330 0700.

We also offer antenatal courses which are a great way to find out more about birth, labour and life with a new baby.

Make friends with other parents-to-be and new parents in your local area for support and friendship by seeing what NCT activities are happening nearby.

Find out more about the condition from the Vasa Praevia charity.

They have a confidential helpline: 07864 698 742 or you can email

NHS. (2018) Vaginal bleeding in pregnancy. Available from: [Accessed 1st January 2018].

RCOG. (2011) Placenta praevia, placenta praevia accrete and vasa praevia: diagnosis and management (Green-top 27), London, RCOG, Available from: [Accessed 8th November 2017].

UK NSC. (2017a) Screening for vasa praevia in the second trimester of pregnancy. Available from: [Accessed 8th November 2017].

UK NSC (2017b) UK NSC recommendation on screening for vasa praevia, Available from: [Accessed 8th November 2017].

Vasa Praevia (2018) Warning signs and symptoms. Available from: [Accessed 1st January 2018].

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