Vasa previa is a rare but serious complication that can occur during pregnancy. It can lead to painless vaginal bleeding, especially late in gestation. It affects only about 1 in 2,500 pregnancies and has a high fetal mortality rate of 60%. Thankfully, there is a 97% fetal survival rate when prenatal diagnosis and elective cesarean delivery before membrane rupture.
There are 3 types of vasa previa:
Type 1: vasa previa with velamentous cord insertion: In some cases, vasa previa occurs with velamentous cord insertion, where the umbilical cord does not insert into the placenta as it should. Instead, the umbilical cord vessels travel outside of the placenta where they are at risk of breaking. If the placenta is sitting low in the uterus near the cervix, the exposed blood vessels are especially vulnerable.
Type 2: vasa previa with a bilobed placenta: Vasa previa can also occur when the placenta splits into two lobes connected by the umbilical cord. If the exposed blood vessels connecting the lobes lie close to the cervix, they can burst and cause bleeding once labor begins.
Type 3: vasa previa with boomerang vessels from the placenta: Vasa previa may also occur with one or more large boomerang vessels that run through the membranes along the margin of the placenta, such as with a resolving placenta previa.
Placenta previa is a condition in which the placenta sits low in the uterus and covers the cervix. Normally, the placenta connects to the top or side of the uterus, away from the cervix. When the placenta is close to the cervix, the blood vessels connecting the placenta and uterus can rupture and bleed when labor starts. A resolved placenta previa or low-lying placenta increases the risk of vasa previa.
Individuals are more likely to have vasa previa if they have:
- Velamentous cord insertions (a pregnancy complication that happens when the umbilical cord from a fetus doesn’t insert into the placenta correctly).
- Marginal cord insertions -especially with aberrant vessels (an abnormal type of umbilical cord attachment during pregnancy).
- Bilobed or succenturiate placental lobes (one or more accessory lobes develop in the membranes apart from the main placenta body in which vessels of fetal origin usually connect them. It is a smaller variant of bilobed placenta).
- Umbilical cord insertion in the lower third of the uterus at the 1st-trimester ultrasound.
- Multiple gestations.
- The use of assisted reproductive technologies (IVF).
83% of the cases of vasa previa had one or more risk indicators in a recent large systematic review of 13 studies (Ruiter L, et al BJOG 2016).
Vasa previa is typically diagnosed during an ultrasound around 18-26 weeks. Those with ultrasound risk factors such as velamentous cord insertion or bilobed placenta may undergo a transvaginal ultrasound to see if there are blood vessels from the umbilical cord near your cervical os (the opening in the cervix at each end of the endocervical canal). Your provider should use the color Doppler feature on the ultrasound to show blood flow more clearly. 3D ultrasound may be further used to clarify the distance of the opening from the cervix.
Vasa previa has been reported to resolve with fetal vessel migration being seen away from the internal cervical opening at rates between 20-40%. This phenomenon is particularly noted when the diagnosis of vasa previa is made at early gestations, the vasa previa is not exactly covering the internal opening, and/or if the vasa previa is not the result of a resolved placenta previa (Klahr R, et al AJOG 2019). The definition of resolution is still debated with distances of the fetal vessel to the internal opening ranging from 2cm, 3 cm, and even 5 cm being considered.
If you are diagnosed with vasa previa, you will likely be scheduled for a c-section delivery. Our team will closely monitor your pregnancy to maximize the amount of time you are pregnant while taking special care to deliver the baby before you run the risk of going into labor. Your specific pregnancy plan will depend on many factors that you should discuss with our team. An organized plan put in place by your provider can improve your chances of a successful delivery and a healthy baby.
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Maternal Fetal Medicine blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!