Vasa Praevia is a rarely (1:2500) reported condition in which fetal blood vessel(s) from the placenta or umbilical cord crosses the entrance to the birth canal, beneath the baby. The condition has a high fetal mortality rate (50-95%). This can be attributed to rapid fetal exsanguination resulting from the vessels tearing when the cervix dilates, membranes rupture or if the vessels become pinched off as they are compressed between the baby and the walls of the birth canal.
The aberrant vessels result from:
Little is known about the cause of these conditions. The most widely recognized theory is called trophotropism. According to Dr. Harris Finberg, trophotropism in placental tissue can be compared to the tendency of a plant to lean towards the sun to get the light it needs to survive. Since the lower segment of the uterus is not as nourishing as the upper segment, the placenta will remodel itself upwards to reach more nourishing tissue.
As the placenta remodels, new growth may occur away from the location where the cord inserts into the placental resulting in velamentous cord insertion. Or the remodeling may leave the placenta in lobes connected by unprotected blood vessels running through the membranes between the lobes (bi-lobed, succenturiate lobed placenta).
Vasa Praevia can result from low-lying placenta or placenta preavia, where the placenta is in front of the birth canal.
Warning Signs of Vasa Preavia
Vasa Praevia might be present if any of the following conditions exist:
- velamentous cord insertion
- bilobed placenta
- succenturiate-lobed placenta
- low-lying placenta or placenta preavia (even if it corrects itself!)
- pregnancies resulting from in-vitro fertilization
- multiple pregnancies
- maternal history of D&C or uterine surgery
When vasa preavia is detected prior to labor, the baby has a much greater chance of surviving. Survival rates can range from 50 -95%, but are coming up as Vasa Praevia is being diagnosed more often.
Vasa Praevia can be detected during pregnancy with use of transvaginal sonography, preferably in combination with color Doppler. Women with the above risk factors should have this test to rule out Vasa Praevia.
When Vasa Praevia is diagnosed, elective delivery by cesarean before labor begins can save the baby’s life. Ideally, it should be performed early enough to avoid an emergency, but late enough to avoid problems associated with prematurity. The IVPF recommends hospitalization in the 3rd trimester, delivery by 35 weeks, and immediate blood transfusion of the infant in the event of a rupture.
Steroid treatments can help accelerate the maturation of the baby’s lungs. An amniocentesis can assess fetal lung maturity.
When there is bleeding during pregnancy, investigation for the source of the blood is necessary. If the blood is determined to be fetal (from the baby), immediate action must be taken to assess the condition of the baby.