Studies show that 56 percent of instances of vasa previa that go undiagnosed result in perinatal mortality or stillbirth. When the condition is detected in pregnancy, however, the fetal survival rate rises to 97 percent.
Risk Factors and Causes of Vasa Previa
Normally, the blood vessels of the umbilical cord and the placenta are insulated inside the amniotic sac. In vasa previa, some of the blood vessels are present in the membranes outside of the sac and therefore don’t benefit from this crucial protection. Causes of vasa previa include: Velamentous insertion of the umbilical cord A velamentous insertion of the umbilical cord is a pregnancy complication in which the umbilical cord inserts itself into the amniotic membrane rather than in the placenta. The baby’s blood vessels then stretch along the membrane between the insertion point and the placenta, leaving them unprotected by the amniotic sac, which normally encases the placenta as well as the umbilical cord. A multi-lobed placenta In rare cases, the placenta is divided into two or three “lobes” by a membrane. Vasia previa can occur when the umbilical cord inserts itself into one of these membranes. It is not known exactly what causes a multi-lobed placenta, but genetics, advanced maternal age, diabetes, a history of chronic seizures, and cigarette smoking or excessive vomiting during pregnancy are thought to be factors. Placenta previa Sometimes the placenta attaches itself to the lower part of the uterus, covering part or all of the cervix. This condition is known as placenta previa, or low-lying placenta. This increases the risk of vasa previa. Pregnancies conceived via IVF, pregnancy with multiples, and prior uterine surgeries may also increase the risk of vasa previa. Having had vasa previa in a previous pregnancy, however, does not appear to be a risk factor.
Symptoms of Vasa Previa
Vasa previa does not always cause symptoms. When it does, the main symptom is the sudden onset of vaginal bleeding, especially in the second and third trimesters. It’s especially worrisome if the blood is very dark or burgundy-colored, as it could indicate that the blood is coming from the fetus, not the mother.
Diagnosing Vasa Previa
Because vasa previa is so rare, it is not intentionally screened for during pregnancy. It will usually be picked up, however, during the routine ultrasound examination performed at 18-20 weeks. If a transabdominal ultrasound, done on the outside of the belly, looks suspicious, your doctor will follow up with a transvaginal ultrasound (in which the transducer is shaped to fit inside the vagina). This, combined with a color Doppler—used to look closely at blood vessels— should confirm the diagnosis. The condition can also be diagnosed during labor, before the membranes rupture. With vasa previa, pulsating vessels can usually be seen running across the bulging membranes upon examination of the cervix.
Treating Vasa Previa
There’s no way to prevent vasa previa. If it can be diagnosed and properly managed during pregnancy, however, it is likely the baby will survive. Typically, your 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 possible, ideally 35 weeks. In some cases, your doctor may want to hospitalize you for the duration of your third trimester for close monitoring and complete bed rest. You may also be given steroids to help the baby’s lungs mature 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. If vasa previa is present, your doctor may recommend a Caesarian section (C-section) between 35 and 37 weeks’ gestation. In a planned C-section, 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. If labor occurs naturally and your membranes rupture spontaneously, then your baby’s blood vessels will almost certainly rupture. If vasa previa is not diagnosed until labor has begun, you will most likely have an emergency C-section. Early delivery carries some risk to the baby, but the risks are much lower than if vasa previa is not detected and labor progresses normally.
A Word From Verywell
Keep in mind that vasa previa, although very frightening, is very rare. When diagnosed early and accurately (even during labor), your chances of having a healthy baby are very good.
