Vasa Previa

Overview

Vasa previa is a rare but serious complication of pregnancy. In this condition, some of the baby's blood vessels run through the membranes near or across the opening of the cervix, instead of being protected inside the umbilical cord or the placenta. Because these vessels are not cushioned, they are vulnerable to compression and tearing.

The greatest danger occurs when the membranes break or during labor, when an unprotected vessel can rupture. Because the blood in these vessels belongs to the baby, even a small amount of bleeding can be life-threatening for the fetus. The good news is that when vasa previa is diagnosed before labor and a cesarean delivery is planned, outcomes are usually very good.

Symptoms

Vasa previa often causes no symptoms during pregnancy and is usually found on a prenatal ultrasound. When complications occur, they typically happen around the time the water breaks or during labor. Warning signs include:

• Painless vaginal bleeding, particularly after the membranes rupture, often bright red.
• Changes in the baby's heart rate, which may be detected during monitoring in labor and can signal that a fetal vessel has been compressed or torn.

Any vaginal bleeding during pregnancy should be evaluated promptly. Bleeding that occurs when the water breaks is an emergency, because it may indicate a ruptured fetal vessel that requires immediate delivery to save the baby.

Causes

Vasa previa happens when fetal blood vessels run across the membranes covering the cervix without the protection of the umbilical cord or placental tissue. This usually results from how the cord and placenta have formed. Common underlying situations include:

• Velamentous cord insertion, in which the umbilical cord attaches to the membranes rather than directly into the center of the placenta, leaving vessels exposed.
• An accessory or extra lobe of the placenta, with connecting vessels that cross near the cervix.
• A low-lying placenta or placenta previa earlier in pregnancy that moves upward, leaving vessels behind near the cervix.

Risk Factors

Some pregnancies are at higher risk for vasa previa, which is why screening is especially important when these factors are present:

• Placenta previa or a low-lying placenta detected earlier in the pregnancy.
• Velamentous cord insertion or an accessory placental lobe.
• Pregnancies conceived through in vitro fertilization (IVF) or other assisted reproductive technology.
• Multiple pregnancy, such as twins or triplets.

When these risk factors are known, clinicians often look carefully for vasa previa during ultrasound examinations.

Diagnosis

Vasa previa is best diagnosed before labor using ultrasound. A standard ultrasound may raise suspicion, and a specialized examination with color Doppler imaging can confirm the diagnosis by showing fetal blood flow in vessels crossing or lying near the cervix. Transvaginal ultrasound provides a clearer view of this area.

Screening is particularly recommended for pregnancies with known risk factors. When vasa previa is confirmed, the pregnancy is monitored closely, and a delivery plan is made well in advance. Early diagnosis is the single most important factor in ensuring a safe outcome.

Treatment

The main goal of management is to deliver the baby safely before labor begins and before the membranes can rupture. When vasa previa is diagnosed in advance, care typically includes:

• Close monitoring during the third trimester, sometimes with hospital admission in the weeks before delivery.
• Corticosteroid medication given to help the baby's lungs mature in case early delivery is needed.
• Planned cesarean delivery scheduled before the due date and before the onset of labor, to avoid the risk of a vessel tearing.

If bleeding occurs or the membranes rupture unexpectedly, an emergency cesarean delivery is performed without delay. Newborns who have lost blood may need a transfusion and close care after birth.

Prevention

Vasa previa itself cannot be prevented, because it depends on how the placenta and cord have formed. However, the serious consequences can largely be prevented through early detection and planning:

• Attend all recommended prenatal appointments and ultrasounds.
• Make sure your care team knows about risk factors such as a low-lying placenta, IVF pregnancy, or a multiple pregnancy.
• Follow the delivery plan made for you, including any recommendation for early hospital admission or a scheduled cesarean.

When to See a Doctor

If you are pregnant, seek immediate emergency care or call emergency services for:

• Any vaginal bleeding, especially bleeding that begins when your water breaks.
• Your water breaking if you have been told you have vasa previa.
• A sudden change or decrease in your baby's movements.

With known vasa previa, do not wait for labor to begin; follow your scheduled delivery plan and contact your care team right away if anything changes. Prompt action is critical, because a ruptured fetal vessel is an emergency for the baby and requires immediate delivery.

Related Topics

Frequently Asked Questions

References

1. American College of Obstetricians and Gynecologists (ACOG).
2. MedlinePlus, U.S. National Library of Medicine.
3. Society for Maternal-Fetal Medicine (SMFM).
4. StatPearls, National Center for Biotechnology Information.