What Is Vasa Previa?

Medically Reviewed by Nivin Todd, MD on April 29, 2023
Written by WebMD Editorial Contributors
3 min read

Vasa previa is a complication that can occur during pregnancy. Some of the blood vessels that connect the umbilical cord to the placenta lie over or near the entrance to the birth canal. When the membranes around the baby rupture, these blood vessels can rupture too. This can cause the baby to lose a lot of blood. The mother may have complications as well. 

There are two main causes of vasa previa: 

Velamentous cord insertion. During pregnancy, your baby is nourished by your placenta through the umbilical cord. The umbilical cord normally attaches to the center of the placenta, and the blood vessels are protected inside of this structure. In velamentous cord insertion, the umbilical cord inserts into the amniotic sac instead of the placenta.   

When blood vessels run through the amniotic sac, they don't have that protection. If the blood vessels in the amniotic sac are above the cervix, it causes vasa previa. 

Bilobed, multilobed, or succenturiate placenta. Your placenta can form two lobes, which is called a bilobed placenta. Rarely, it can form more than two lobes, which is called multilobed. Sometimes a smaller lobe, called a succenturiate lobe, forms. Vasa previa happens if the blood vessels that run between these lobes end up lying against the cervix.

A bilobed, multilobed, or succenturiate placenta can occur if the placenta implants in one of the following places:

  • Over a fibroid in your uterus
  • Area of decreased blood supply
  • Area of previous surgery
  • Over the cervix

When your baby is ready to be born, the amniotic sac ruptures. The baby then moves through the cervix and out through the vagina. If you have vasa previa, the rupture of the amniotic sac will also rupture the blood vessels. This will cause your baby and possibly you to lose a lot of blood. 

There are often no symptoms associated with vasa previa until labor starts. Some women have painless vaginal bleeding that is dark in color. Because your baby's blood doesn't have as much oxygen in it as yours does, it appears darker.  

In vasa previa that hasn't been found before labor, the symptoms include vaginal bleeding after your membranes rupture. Your baby may also have a slow heartbeat. 

Vasa previa is associated with the following conditions: 

Your doctor may suspect you have vasa previa based on ultrasounds done as part of your routine prenatal care. If so, they will do a transvaginal ultrasound, which is done with a wand inserted into your vagina, to verify it. You may also have a doppler color flow mapping test done. This test lets your doctor see where your blood vessels are. 

The goal of treatment for vasa previa is to safely prolong your pregnancy but deliver your baby early enough to avoid rupturing the blood vessels. Treatment may include: 

  • Monitoring your baby with nonstress tests twice a week, starting between 28 and 32 weeks.
  • You may be admitted to the hospital between 30 and 32 weeks to more closely monitor the baby.
  • You may be given a shot of corticosteroids to help your baby's lungs mature.
  • Pelvic rest may be advised, which means avoiding sex or putting anything in your vagina.
  • Planned C-section delivery between 34 and 37 weeks.
  • You may need an emergency C-section if your membranes rupture early, you have vaginal bleeding, or your baby is in distress.

Vasa previa is very rare. It only occurs in about 1 in 2500 pregnancies. If it's diagnosed before labor, monitored, and you have a C-section, there's a 97% chance that your baby will be fine.   

Most babies who are born vaginally to mothers with vasa previa will die, which is why delivery by C-section is so important. The rupture of the blood vessels causes the baby to lose too much blood. A vaginal delivery can also pinch the blood vessels, which cuts off the blood flow to the baby. This can cause brain damage.