Vasa previa is an uncommon pregnancy complication where unprotected blood vessels from the placenta pass over or near the cervix. If left untreated, these vessels can rupture when a pregnant person’s water breaks or during vaginal delivery, putting the fetus at risk of severe blood loss. With vasa previa, a cesarean delivery is necessary before labor begins on its own to prevent the vessels from rupturing during delivery.
Certain conditions and circumstances can increase the risk of developing vasa previa. These include:
While these factors increase the risk of vasa previa, the condition can occur in pregnancies without any of these conditions.
No one knows exactly what causes vasa previa. In a normal pregnancy, the umbilical cord runs from the fetus to the placenta — an organ that develops during pregnancy and plays a crucial role in supporting the growth and development of the fetus by providing oxygen and nutrients to the fetal vessels in the placenta. The umbilical cord consists of three fetal blood vessels that are protected by a thick, gelatinous substance. In vasa previa, the fetal blood vessels from the umbilical cord enter into the membranes that surround the fetus rather than into the placenta. These fetal vessels aren’t protected and run through the membrane over the cervix. Therefore, when the membranes rupture, as happens in labor, these fetal vessels often burst, putting the fetus at risk of severe, life-threatening bleeding.
Vasa previa typically has no symptoms before the membranes surrounding the fetus rupture. The first sign of vasa previa, if not found before labor, is typically bleeding at the time the membranes rupture. This fetal blood loss can cause abnormalities in fetus's heart rate and, if bleeding is severe, can result in fetal death.
Vasa previa is diagnosed during pregnancy through ultrasound.
Vasa previa can be screened for during an anatomy scan, which usually takes place between 18 and 20 weeks of gestation and checks for any abnormalities in the fetus’s development.
Prenatal screening for vasa previa using transvaginal or abdominal ultrasound is highly accurate. If vasa previa is detected during the anatomy scan, we advise confirming the diagnosis with an additional transvaginal ultrasound later in pregnancy because, in some cases, vasa previa may resolve as the pregnancy progresses.
Because vasa previa puts a fetus at a high risk of severe bleeding, it’s important to find it early so it can be closely monitored and managed.
The Fetal Care and Surgery Center is constantly looking to advance the diagnosis, management, and treatment of vasa previa. Our team has published papers that investigate how it develops and how it progresses over time, as well as negative prenatal outcomes after vasa previa is diagnosed.
During fetoscopic laser photocoagulation (FLP), doctors insert a thin, straw-like tube (a scope) into the womb and use a laser to clot the blood vessels that pass over the cervix. This stops the blood flow within those vessels, addresses the problem of unprotected vessels passing over the cervix, and can prevent the risk of fetal death from the rupture of those vessels during labor. This procedure can be offered to a very specific group of patients with type II and III vasa previa.
FLP is typically performed between 30 to 33 weeks of gestation. It is a one-day procedure, meaning patients can typically return home the same day or one day after the intervention. Following a successful FLP treatment, patients can continue their pregnancy under the care of their primary prenatal provider and can expect a vaginal delivery barring unforeseen circumstances or unless otherwise discussed with their obstetric care team.
Because vasa previa puts a fetus at a high risk of severe bleeding, it’s important to find it early so it can be closely monitored and managed. Through the collaborative work of fetal surgeons, maternal-fetal medicine specialists, and other specialized care providers, the Boston Children’s Fetal Care and Surgery Center is at the forefront of diagnosing and treating vasa previa and other fetal health concerns.
