What is vasa previa?

General risk factors for vasa previa include (1, 2, 3):

• Pregnancies resulting from in-vitro fertilization (IVF)
• Multiple gestation (i.e. twins, triplets, etc.)
• Low-lying placenta or placenta previa (even if it corrects itself)
• Maternal history of D&C (dilation and curettage), cesarean delivery, or other uterine surgery

There are two main causes/types of vasa previa (2):

1. Velamentous cord insertion (type 1 vasa previa): The umbilical cord fails to insert into the appropriate part of the placenta, instead attaching to fetal membranes. The fetal vessels can still connect to the placenta, but must do so without the protection of the umbilical cord.
2. Multi-lobe placenta (type 2 vasa previa): Sometimes, the placenta is divided into two or more parts, called “lobes.” The fetal vessels connect the lobes together, but have to venture outside of the umbilical cord, putting the infant at risk.

When vasa previa is present, the baby’s health depends on a timely prenatal diagnosis and planned C-section delivery. If medical professionals fail to recognize this condition and wait for the mother to deliver vaginally, sudden and severe bleeding will occur. This is because when the amniotic sac ruptures, the fetal vessels will rupture along with it. This is a medical emergency and necessitates emergency blood transfusions after birth.

During prenatal visits, physicians use ultrasounds to check for significant problems with the major vessels involved in uteroplacental circulation, including those in the umbilical cord. Vasa previa can be detected by a transvaginal ultrasound coupled with use of color Doppler (1). Routine ultrasounds are important in any pregnancy, but doctors should be especially thorough in examining patients with risk factors for vasa previa (velamentous cord insertion, multi-lobe placenta, placenta previa, IVF, multiples pregnancy, etc.). The characteristic sonographic finding used to diagnose vasa previa is of membranous vessels that cross the mother’s cervical opening (2).

Vasa previa that is present during the second trimester may resolve over time. Usually, though, vasa previa persists and the vessels are at risk of rupturing (4).

Once vasa previa is diagnosed, care standards dictate that the mother should have serial nonstress tests to look for any evidence of umbilical cord compression. Due to the increased risk of preterm delivery and associated complications, a steroid called betamethasone should be given between 28 and 32 weeks of gestation to help the baby’s lungs and other tissues mature. In addition, the mother should be admitted to the hospital between weeks 30 and 34 for more frequent fetal heart rate monitoring and to enable immediate intervention if it becomes necessary. At this point, nonstress tests should be performed two to three times a day. A scheduled C-section is typically indicated at about 34-35 weeks of gestation. Exact guidelines vary, but it is important to balance the risks associated with amniotic sac rupture (which in cases of vasa previa also causes vessel rupture) and the risk of complications associated with prematurity.

In cases of vasa previa, an emergency C-section delivery should be performed if any of the following occur:

• Premature labor
• Premature rupture of the membranes (PROM)
• Nonreassuring fetal heart tracings, especially repetitive variable decelerations not helped by medications given to suppress labor (tocolytics)
• Vaginal bleeding accompanied by nonreassuring fetal heart tracings such as a fast heart rate (tachycardia) or a sinusoidal heart rate pattern, or evidence of pure fetal blood

Unfortunately, vasa previa may go undiagnosed if proper testing is not performed and diagnosis made. Vasa previa should be suspected when a woman bleeds at the time of membrane rupture. If a baby’s heart rate is non-reassuring, a C-section delivery must occur within a matter of minutes to prevent major damage.

When vessels rupture, it is critical that members of the medical team quickly order blood products for the baby in case a transfusion is needed after C-section delivery. Transfusions are often life-saving when a baby is affected by vessel rupture caused by vasa previa (2).

Some infants die during birth as a result of undiagnosed vasa previa. Babies born vaginally are also at high risk of profound blood loss, reduced circulation, and birth asphyxia (fetal oxygen deprivation) (2). This can lead to a number of birth injuries and permanent disabilities, including the following:

• Hypoxic-ischemic encephalopathy (HIE). HIE is a type of brain damage caused by a reduction in the flow of oxygenated blood.
• Periventricular leukomalacia (PVL). PVL is damage to the brain’s white matter.
• Permanent brain damage
• Seizure disorders
• Cerebral palsy (CP)
• Intellectual disabilities
• Developmental delays
• Motor disorders
• Microcephaly

The information presented above is intended only to be a general educational resource. It is not intended to be (and should not be interpreted as) medical advice. If you have questions about managing vasa previa, please consult with a medical professional.

1. Everything You Need to Know About Vasa Previa (2017). Retrieved March 7, 2019, from https://www.healthline.com/health/pregnancy/vasa-previa
2. (n.d.). Retrieved March 12, 2019, from https://www.uptodate.com/contents/velamentous-umbilical-cord-insertion-and-vasa-previa
3. Vasa Previa: Symptoms, Management, and Treatment. (n.d.). Retrieved March 12, 2019, from https://www.healthline.com/health/pregnancy/vasa-previa#causes-and-risk-factors
4. Studio, B. K. (n.d.). Publications & Guidelines | SMFM.org – The Society for Maternal-Fetal Medicine. Retrieved May 28, 2024, from https://www.ajog.org/article/S0002-9378%2815%2900897-2/fulltext