Vasa previa is an extremely rare but devastating condition in which fetal umbilical cord blood vessels cross or run in close proximity to the inner cervical os (the internal opening in the cervix separating the uterine cavity from the vagina). These vessels course within the membranes, unsupported by the umbilical cord or placental tissue, and are at risk of rupture if the supporting membranes are damaged. Vasa previa carries a high mortality rate—50percent of undiagnosed cases end in the death of the fetus. Fortunately this condition is rare, occurring in only one out of every 2,000 pregnancies.
The normal umbilical cord begins right off the placenta, and it carries two arteries and one vein directly into the baby’s body. In vasa previa, the origin of the cord is in the membranes near the placenta, so there is an area in the membranes where the blood vessels are not in the cord at all. Even worse, this area of the membranes containing the cord blood vessels is in front of the internal cervical os. Without the protection of the tough, fibrous cord, the blood vessels have little support. When labor begins and the mother’s water breaks, the unsupported vessels in and around the umbilical cord can tear, resulting in the death of the baby from blood loss within two to three minutesunless an emergency caesarean section is performed.
If you are having difficulty grasping what occurs in vasa previa, it may be helpful to understand the origin of the condition’s name, which is derived from Latin. Vasa is the plural form of vas, which denotes a vessel (it’s the root of English words like vase), and previa (from which we also get previous) can be broken down into two components—pre, meaning before, and via, meaning way. Vasa previa can therefore be understood to mean roughly, “vessels in the way of the baby.”
Causes of Vasa Previa
Due to its rarity, vasa previa has not been well studied. Some experts believe that it may occur when the nutrients at the bottom of the placenta are not as rich as the ones at the top of the placenta. As a plant would grow towards the sun, these experts think the blood vessels grow toward the better nutrition. The theory behind this hypothesis is called Trophotropism.
Unfortunately, no one really knows for sure what causes vasa previa, although there are similarities shared by many cases; women who have suffered vasa previa often have:
- Low-lying placentas
- Previous pregnancies delivered by C-section
- Pregnancies assisted by in vitro fertilization (IVF)
- Placentas that consist of more than one piece (see below)
The reason for the association of IVF with vasa previa is not clear, but incidences have been reported to be as high as one in 300 for such pregnancies—much higher than the rate of one in 2,000 reported among the general population.
The condition of low-lying placenta (also known as placenta previa) is also associated with vasa previa, and these two conditions together seem to create and additional risk that the baby will assume a transverse or breech position. This is because the placenta’s position in the lower part of the uterus gets in the way of the baby’s head, preventing the baby from assuming the correct “head-down” position.
Vasa Previa Symptoms
Unfortunately, in some cases there are no warning signs of vasa previa, which generally can’t be diagnosed until labor, when the fetus is already at risk, or until after a stillbirth. Expectant mothers should watch for the sudden onset of painless vaginal bleeding, especially in their second and third trimesters. A telltale clue is the color of the blood. Bright red blood is well oxygenated, and this means it comes from the mother, not the baby. The baby’s blood is a darker red color due to the naturally lower oxygen levels of a fetus. If you see very dark burgundy blood when the water breaks, this may be an indication of vasa previa.
Vasa previa may be present if any of the following conditions exist:
- Velamentous cord insertion—an umbilical cord abnormality occurring in about 1–2 percent of pregnancies, in which the cord inserts into the fetal membranes and travels through them to the placenta, rather than inserting directly into the placenta
- Bi-lobed placenta—the placenta is divided into two separate pieces called lobes
- Low-lying placenta, also known as placenta previa
- Multiple fetuses (twins, triplets, etc.)
- Mother has previously had uterine surgery
Vasa Previa Treatment
If your doctor is able to diagnose vasa previa early on, chances of survival for you and your baby are in the neighborhood of 97percent. The condition can be detected through the use of transvaginal sonography combined with color Doppler. If your doctor feels you have any of the warning signs listed above, he or she will probably recommend that you have this test done to rule out vasa previa.
After diagnosis, the next steps depend on how far along the pregnancy is. Your doctor may decide to deliver your baby via C-section sometime between the 35th and 37th week of pregnancy, and the medical team attending the delivery will probably be prepared to provide an immediate blood transfusion for the baby in the event of a rupture. It is possible that your doctor will also recommend that you be hospitalized throughout your third trimester. Steroids are sometimes used to mature the lungs of the fetus in the event it must be delivered prematurely; amniocentesis can be used to determine whether this is necessary.
Talking to Your Doctor
Here are some questions you can ask your doctor about vasa previa:
- Based on my medical history, do you think I may be at risk for vasa previa?
- Do you recommend a C-section delivery for my baby?
- Does having vasa previa in one pregnancy make it likely that condition will recur in future pregnancies?
- Do you recommend a transvaginal sonography test?