What is vasa praevia?
In most pregnancies, blood vessels from the umbilical cord insert directly into the placenta. In vasa praevia, these vessels are not protected by the umbilical cord or the placenta tissue. Instead, they go across the entrance to the birth canal, beneath the baby.
These blood vessels are very delicate. If they tear when you are in labour or when your waters break, this can cause blood loss.
This can be dangerous because the blood that is lost comes from your baby. Babies only have a small amount of blood in their bodies so they can become very unwell or even die if this happens.
How common is vasa praevia?
Vasa praevia is very rare, affecting between 1 in 1,200 and 1 in 5,000 pregnancies.
How is vasa praevia diagnosed?
We don’t know why vasa praevia happens, but we do know the risk of having it is higher if:
- you are having an IVF pregnancy
- you have a low-lying placenta
- you are carrying more than one baby
- your placenta or umbilical cord develop in an unusual way.
Vasa praevia is not routinely checked for during pregnancy. However, if any of these factors apply to you, you may be offered an extra scan during your pregnancy to check whether you have vasa praevia.
Some women don’t have any symptoms and some women may have vaginal bleeding. If you have any bleeding during your pregnancy, with or without pain, it’s very important to get it checked out.
If your doctor thinks you have vasa praevia in your first trimester, you will be scanned again during your second trimester to confirm it.
You may also be diagnosed early if you have a scan because of the risk factors above, or during early labour if:
- you have a vaginal examination
- you have vaginal bleeding
- your baby is in distress after your waters break.
Tell your maternity unit immediately if your waters break and
- the waters are smelly or coloured
- you're losing blood.
This could mean you and your baby need urgent attention.
If vasa praevia is diagnosed during pregnancy, the chances of the baby’s survival is over 97%.
How is vasa praevia treated?
If you are diagnosed with vasa praevia before you go into labour, you should be offered a planned caesarean section at around 34–36 weeks of pregnancy. This would mean that your baby would be born prematurely, so you will be offered a course of steroids (two injections, 12–24 hours apart) to help your baby’s lungs and other organs to mature.
If your healthcare professional suspects that you may have vasa praevia when you go into labour or when your waters break, your baby needs to be born urgently, usually by emergency caesarean section.
Can I do anything to prevent vasa praevia?
Unfortunately, no. If you are diagnosed with vasa praevia during pregnancy, your healthcare professional may advise you to stay in hospital from 30-32 weeks until the end of your pregnancy as a precaution.
Jauniaux E et al (2017) Prenatal diagnosis and management of vasa previa in twin pregnancies: a case series and systematic review. Jun;216(6):568-575. doi: 10.1016/j.ajog.2017.01.029. Epub 2017 Jan 30.
Royal College of Obstetricians and Gynaecologists (2018) Placenta praevia, placenta accreta and vasa praevia https://www.rcog.org.uk/globalassets/documents/patients/patient-information-leaflets/pregnancy/pi-placenta-praevia-placenta-accreta-and-vasa-praevia.pdf
Derbala, Y (2007) Vasa previa. Journal of prenatal medicine. Jan-Mar; 1(1): 2–13.
NHS Choices. Signs that labour has begun. https://www.nhs.uk/conditions/pregnancy-and-baby/labour-signs-what-happens/#what-happens-when-my-waters-break (Page last reviewed: 09/11/2017. Next review due: 09/11/2020)
ERM J et al on behalf of the Royal College of Obstetricians and Gynaecologists (2018) Vasa Paevia: Diagnosis and Management. Green-top Guideline No. 27b. BJOG An International Journal of Obstetrics and Gynaecology