What Is Vasa Previa?

Vasa previa occurs when unprotected umbilical cord blood vessels run very near or over the opening of the cervix. Vasa previa is Latin, and it translates loosely to "vessels in the way" of the birth canal. 

The main risk of vasa previa is that umbilical blood vessels can rupture when the amniotic sac breaks. Someone with a low-lying placenta is at the greatest risk of vasa previa.

Vasa previa poses no health risks to the pregnant person, but it poses a grave risk to the fetus. Undiagnosed, it can lead to stillbirth. When diagnosed in pregnancy, survival rates are high.

Signs/Symptoms of Vasa Previa

Vasa previa does not often have any symptoms in pregnancy. Occasionally, it can present as vaginal bleeding. If bleeding does occur, it usually happens in the second or third trimester.

If not discovered through standard diagnostic prenatal tests, symptoms most often present in labor. Symptoms of vasa previa in labor include vaginal bleeding followed by fetal distress. When this occurs, it can take less than 10 minutes for the fetus to experience fatal blood loss.

Causes

Connective tissue known as Wharton’s jelly surrounds the arteries and veins of the umbilical cord. In vasa previa, however, the section of umbilical cord that runs over the opening of the cervix is exposed. This may happen as a result of abnormal placement of the umbilical cord in the placenta.

Velamentous Insertion

Velamentous insertion is a pregnancy complication in which the umbilical cord attaches to the chorioamniotic membrane, rather than the placenta. In this case, a segment of the umbilical cord runs between the amnion and chorion (the inner and outer layer of the amniotic sac, respectively).

When vasa previa occurs as a result of velamentous insertion, it is known as type I.

Multi-Lobed Placentas

Bilobed and trilobed placentas may also lead to vasa previa. With multi-lobed placentas, the umbilical cord can insert into the membranes between the placentas. Other times it inserts into the larger of the two placentas.

Vasa previa can occur when the vessels run between the lobes and over the cervical opening. When vasa previa occurs as a result of multi-lobed placentas, it is known as type II.

Diagnosis

Since vasa previa does not often present with symptoms before labor, it is not always detected early. However, studies have found that when it is diagnosed early by ultrasound, perinatal mortality is reduced from 56% to 3%.

Vasa previa may be detected during a routine ultrasound exam done in the second trimester. If vasa previa is suspected, a follow-up ultrasound in the third trimester is recommended.

During the ultrasound, the technician will look for where the umbilical cord inserts. Transvaginal ultrasound, three-dimensional (3D) ultrasound, and color doppler ultrasound may help your healthcare provider get a closer look at the umbilical vessels and placental attachment.

Magnetic resonance imaging (MRI) can be used to help confirm the diagnosis if it is uncertain. Even if the cord presentation is unclear, if your practitioner sees risk factors for vasa previa, like a low-lying placenta or abnormal cord insertion, they may diagnose vasa previa. 

Treatment

It is not possible to prevent vasa previa. However, when diagnosed during pregnancy and carefully managed, fetal survival rates are high.

The goal of management during pregnancy is to carry the pregnancy while avoiding the spontaneous rupture of membranes. Some recommend hospitalization beginning at 30 weeks to closely monitor signs of labor and intervene with a cesarean immediately, but there is no data to support it as a standard practice.

Studies have found that a planned cesarean section between 34 and 37 weeks is reasonable. If your healthcare provider recommends delivering your baby on the earlier end of the range, they may prescribe corticosteroids at 28 to 32 weeks in order to help develop the fetal lungs.

Risk Factors

Vasa previa is a very rare complication of pregnancy, affecting 1 in 2,500 pregnancies. While it has a high perinatal survival rate when diagnosed prenatally, the perinatal mortality rate is as high as 60% when not diagnosed prior to labor.

Some things that put you at a higher risk of vasa previa include:

• Placenta previa, a condition in which the placenta lies over the cervix
• Low-lying placenta
• In vitro fertilization (IVF)
• Carrying multiples
• Velamentous cord insertion
• Multi-lobed placenta
• Prior uterine surgery or dilation and curettage (D&C)

Complications

The biggest danger with vasa previa is rupture of the amniotic membranes. When the amniotic sac breaks, this can cause the unprotected veins and arteries of the umbilical cord to rupture as well, leading to fetal hemorrhage. 

When vasa previa is detected during pregnancy, your healthcare provider will monitor you closely to make sure your baby is delivered via c-section before your bag of waters is likely to rupture spontaneously.

When vasa previa isn’t detected until labor, it is often after the bag of waters has ruptured. In that case, vaginal bleeding and fetal distress soon follow. An emergency cesarean is required when vasa previa is discovered during labor.

Fetal hemorrhage resulting in exsanguination (death caused by blood loss) can occur with vasa previa. Perinatal mortality is exponentially higher in cases where vasa previa isn’t diagnosed until labor. Vasa previa that is diagnosed during pregnancy has a high survival rate.

A Word From Verywell

Vasa previa is a very serious complication of pregnancy. It is natural to feel worried if your healthcare provider has told you that you have vasa previa. The good news is that standard ultrasounds in the second trimester are often able to detect vasa previa or risk factors that make vasa previa more likely. 

Be sure to tell your practitioner if you have any vaginal bleeding, as it could be a sign of vasa previa. If you have been diagnosed with vasa previa or if your healthcare provider suspects you may have vasa previa, it is important to monitor your pregnancy very closely. Remember, when a diagnosis is made prenatally, outcomes are very good.