What is vasa previa?
Vasa previa is an incredibly rare, but severe, complication of pregnancy. In vasa previa, some of the 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.
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 rise to 97 percent.
What are the symptoms?
In many cases, there are no symptoms of vasa previa at all. It often goes undetected until labor, when the fetus is already distressed, or following a stillbirth.
Pregnant women should seek immediate medical attention if they have any painless vaginal bleeding. A sign that a woman might have vasa previa is if the blood is very dark, a burgundy red. The blood of a fetus is naturally lower in oxygen than that of the mother. So if the blood is darker than what is typical, it could indicate that it has come from the fetus and not the mother.
Causes and risk factors
One cause of vasa previa is an umbilical cord abnormality called velamentous cord insertion. This is when the umbilical cord goes into the membranes, resulting in vessels that are unprotected leading to the placenta. Another cause is bilobed placenta, where the placenta is in two pieces. In these cases, the vessels may be unprotected where they cross between the two lobes.
You’re at greater risk of vasa previa if:
- your placenta is low-lying (placenta previa)
- your previous birth(s) were by cesarean delivery
- your pregnancy occurred through in vitro fertilization (IVF)
- you’re pregnant with multiple babies
- you’ve had previous uterine surgery
How is it diagnosed?
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 shaped to fit inside a woman’s vagina. It 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.
How is it treated?
There’s no way to prevent vasa previa. But if it can be diagnosed before delivery, then with proper management the chances of survival for the baby are excellent.
In some cases, vasa previa may resolve during pregnancy. If you’ve been diagnosed with vasa previa in your pregnancy, then your care provider will offer regular follow-up ultrasounds to monitor the condition closely. 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.
At the delivery of your baby, there will be a team on hand that can give your baby a blood transfusion in the event that there is a rupture of the blood vessels. If one of the blood vessels is torn, then your surgeon may want to clamp the cord immediately to help minimize the amount of blood that your baby loses.
What’s the outlook?
Vasa previa doesn’t pose any physical health risks to the mother, but the risks to 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 are 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 is 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 a very high chance your baby will be just fine.