Vasa previa is an extremely rare, but severe, complication of pregnancy. In vasa previa, some fetal umbilical cord blood vessels run across or very close to the internal opening of the cervix.

These vessels are inside the membranes, unprotected by the umbilical cord or the placenta. As such, they are at risk of rupturing when the membranes break, for example with the onset of spontaneous labor or preterm labor.

In terms of risk, 56 percent of instances of vasa previa that go undiagnosed result in stillbirth. However, when the condition is detected in pregnancy, the chances of survival for the fetus can rise to 97 percent.

If vasa previa is not diagnosed during the routine midpregnancy obstetrical anatomy ultrasound, it often goes undetected until labor when the fetus may show signs of significant distress, or following a stillbirth.

It is standard to assess the placenta location and umbilical cord at the midpregnancy ultrasound, and when a variance is suspected, additional testing and follow-up is recommended.

If the vasa previa does not resolve, early delivery via cesarean section is most often advised. This is recommended to avoid the onset of labor or ruptured membranes, which can be associated with rapid and significant fetal blood loss.

Pregnant people should seek immediate medical attention if they have any painless vaginal bleeding.

The cause of vasa previa is unknown, but it is thought to develop in the same way as a velamentous cord insertion, which is when the fetal blood vessels are unprotected in the membranes rather than being protected by Wharton’s jelly. This results in unprotected fetal blood vessels leading to the placental end of the umbilical cord.

Another risk factor for vasa previa is a bi-lobed placenta, where the placenta is in two pieces. In these cases, the vessels may be unprotected where they cross between the two lobes.

A greater risk of vasa previa tends to be more common if the:

The best method for detecting vasa previa is to do a transvaginal scan combined with a color Doppler. A transvaginal scan is internal.

The transducer that produces the ultrasound waves is a thin straight probe, which is inserted into the vagina by the sonographer, such that a portion sits inside the vagina (a few inches) and the rest of the wand or transducer remains out of the body.

The probe will be lubricated and covered with a sheath. It’s far more accurate than using an abdominal scan, as it allows the sonographer to see the area of interest clearly.

If the image is viewed in grayscale, it can be difficult to read. This is where the color Doppler comes in. This technique allows color to be added to the image to enable the technician to see which way the blood is flowing and at what speed.

Because of the rarity of this condition, it’s not routinely screened for. Your doctor will probably recommend these tests if you have one or more of the risk factors described above.

There’s no way to prevent vasa previa. But if it can be diagnosed before delivery, the chances of survival for the baby can usually be excellent with proper management.

In some cases, vasa previa may resolve during pregnancy. If you’ve been diagnosed with vasa previa in your pregnancy, it’s important to ensure your healthcare professional will offer ongoing regular follow-up ultrasounds, discussion, and planning for an early scheduled cesarean section.

The aim in managing the condition is to allow the pregnancy to progress for as long as safety allows. Your doctor will be able to help you balance the risks of early delivery with the risks of labor and rupture of the membranes.

In some cases, your doctor may recommend hospitalization for the duration of your third trimester for close monitoring and complete bed rest. Pelvic rest is often suggested, which means that nothing should be placed inside the vagina and you shouldn’t have sex.

You may also be given steroids to help mature the baby’s lungs in case they need to be delivered early. Your doctors will individualize your plan of care depending on your risk factors, ultrasound findings, and other factors.

It’s usual for your doctor to recommend cesarean delivery between 35 and 37 weeks’ gestation in cases of vasa previa. This is because if labor occurs and your membranes rupture spontaneously, then your baby’s blood vessels will almost certainly rupture also, causing your baby to bleed.

In a planned cesarean delivery, your surgeon will be able to adjust the type and placement of the incision according to where your placenta and your baby’s blood vessels are.

When vasa previa is not diagnosed during the prenatal period, spontaneous labor or rupture of the membranes can lead to serious health concerns due to severe fetal hemorrhage, including:

  • fetal or neonatal death
  • severe fetal anemia requiring transfusions
  • cerebral palsy

Vasa previa doesn’t pose any physical health risks to the birthing parent, but the risks for the baby can be significant and can ultimately result in the loss of their life.

More than half of all cases of vasa previa that aren’t detected in pregnancy result in stillbirth. However, if the condition is diagnosed in pregnancy, then the chances of survival for the baby can typically be excellent.

It’s important to remember that while this condition is cause for concern, it’s also very uncommon. The largest studies report that vasa previa is only found in up to 4 of 10,000 pregnancies.

Your medical team will typically be aware of the risk factors for the condition and will recommend tests if they feel it necessary. With antenatal diagnosis and proper management, there is usually a very high chance your baby will be just fine.