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Vasa Previa

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Updated January 15, 2009

Placenta

In a normally developing placenta, the cord and blood vessels insert into the placenta, but vasa previa may involve an umbilical cord that inserts into the side of the sac with blood vessels growing along the membranes to connect it to the placenta.

Image © A.D.A.M.

What is Vasa Previa?:

Vasa previa is a serious pregnancy complication that occurs in an estimated 1 in 2,500 pregnancies. In vasa previa, blood vessels involved in the baby's circulation grow along the membranes in the lower part of the uterus at the cervical opening. When the condition is not detected in advance, the blood vessels can rupture during labor.

Causes of Vasa Previa:

In a normal pregnancy, the blood vessels of the umbilical cord and the placenta are insulated inside the amniotic sac. In vasa previa, blood vessels are present at the membranes without this protection due to either velamentous insertion of the umbilical cord or an abnormally formed multi-lobed placenta.

Vasa previa of either type can develop as a complication of placenta previa, or a low-lying placenta, being present or having been present at some point during the pregnancy. A velamentous umbilical cord or multi-lobed placenta that exists higher in the uterus would not necessarily mean vasa previa.

Why Vasa Previa Is Dangerous?:

When a woman with vasa previa goes into labor and the cervix begins to dilate, the blood vessels present at the cervix can rupture. If this occurs, the baby will experience rapid blood loss and may die before doctors are able to do anything about the situation. When vasa previa is not diagnosed before the onset of labor, the chance of stillbirth may be as high as 95%.

Beside outright rupture, the blood vessels crossing the cervix can easily become compressed when the baby drops further down in the pelvis, decreasing the baby's blood supply and causing drops in the heart rate.

Diagnosis of Vasa Previa:

Vasa previa usually causes no outward symptoms during the pregnancy, but doctors can pick up markers for the condition as early as the second trimester via ultrasound. Following up a standard ultrasound with a color Doppler ultrasound can give doctors a good idea whether vasa previa is present.

Risk Factors:

Pregnancies involving known placenta previa, velamentous cord insertion, or multi-lobed placenta may be at risk for vasa previa. In addition, multiple pregnancies or pregnancies conceived via IVF are at increased risk. Vasa previa in a previous pregnancy does not appear to be a risk factor.

Treating Vasa Previa:

When doctors are able to diagnose vasa previa early in the pregnancy before the onset of labor, mothers may be hospitalized in the third trimester to ensure rapid access to medical care should blood vessels rupture. The doctor will most likely perform a c-section around 35 weeks of pregnancy.

This strategy drastically improves the odds that the baby will survive. Early delivery carries some risk to the baby because of normal consequences of prematurity, but the risks are much lower than if the vasa previa is not detected and labor progresses normally.

Sources:

International Vasa Previa Foundation, "FAQ." Accessed 30 Jun 2008.

Lee, Wesley, Virginia L. Lee, Janet S. Kirk, Christopher T. Sloan, Ramada S. Smith, and Christine H. Comstock, "Vasa Previa: Prenatal Diagnosis, Natural Evolution, and Clinical Outcome." Obstetrics & Gynecology 2000. Accessed 30 Jun 2008.

Oyelese, Yinka, and John C. Smulian, "Placenta Previa, Placenta Accreta, and Vasa Previa." Obstetrics & Gynecology 2006. Accessed 30 Jun 2008.

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