This leaflet is to help you understand what Vasa Previa is and what causes it, what tests you need and what treatments will be available to you during pregnancy.

What is Vasa Previa?

Typically vessels from the baby to the placenta directly enter the placenta and are not seen to run through the membranes on their way to the placenta. Vasa previa is a rare condition in which fetal vessels run through the membranes and are seen close to or crossing the cervix.

 Why does vasa previa happen? 

The exact cause for vasa previa is unknown. It may result from a velamentous cord insertion (when the umbilical cord inserts in the membranes rather than directly into the placenta), as a result of a succenturiate placenta (placenta has two separate parts and vessels run between them) or as a result of a large vessel just past the edge of a placenta. 

What is the associated risk with the vasa previa? 
When vessels are located in the lower portion of the uterus or near the cervix, there is a high risk of tearing of these fetal vessels if the membranes (bag of water) ruptures. This can lead to serious fetal bleeding (fetal hemorrhage) and unfortunately death. 

How is vasa previa diagnosed? 

Diagnosis is made with ultrasound. The diagnosis can usually be suspected with routine ultrasound. If a vasa previa is suspected, you may be asked to have a vaginal ultrasound to look more closely at the cervix and at the structures in the lower part of the uterus. Ultrasound with colour Doppler, which can tell if the structures contain blood flow, will help to identify fetal vessels close to or crossing the cervix.
Which pregnancies are at higher risk? 

Pregnancies with these conditions are at higher than average risk for having a vasa previa: 

  • Velamentous cord insertion (umbilical cord inserts into the membranes (bag of water) and not directly into the placenta)
  • Placenta previa or low-lying placenta (placental edge covering or near the cervix (birth canal))
  • Succenturiate or bilobed placenta (placenta is formed in two pieces)
  • In vitro fertilisation 
  • Multiple gestations (twins, triplets)

Vasa previa can happen in any pregnancy. 

Are there signs or symptoms suggestive of vasa previa? 

Most women with a vasa previa have no symptoms. A pregnant woman who has lots of vaginal bleeding after the rupture of membranes may be at risk of this condition, especially if there is an abnormal fetal heart rate after an episode of rupture of the fetal membranes with bleeding. This is a true emergency, which requires immediate delivery.

How will the pregnancy be managed? 
Since vasa previas are rare, the best way to manage these pregnancies is not known. The most important factor in having a healthy baby is identifying the vasa previa so that you and your doctor can discuss how best to manage the pregnancy and make delivery plans.

Some options for management of pregnancy include: 

  • Hospitalisation in the preterm period, usually starting between 28-32 weeks of gestation until delivery
  • Measurement of cervical length
  • Corticosteroids for fetal lung maturity are recommended 
  • Delivery by Caesarean section prior to the onset of labour

Will it happen again? 

The chance that you have another pregnancy affected by vasa previa is unknown. In another pregnancy you may wish to have your doctor look for vasa previa with ultrasound.  

What other questions should I ask?

  • Are there any other abnormalities on the ultrasound?
  • How often will I have ultrasound examinations done?
  • Where should I deliver?
  • At what gestational age should I deliver? 
  • Can I meet the team of doctors that will be assisting my baby when it is born, prior to delivery?

Last updated July 2023