Vasa Previa

Fetal blood vessels are normally protected by the umbilical cord or placenta. Vasa previa is a rare but serious condition in which unprotected fetal blood vessels run through the fetal membranes that surround the fetus and lie across the cervix. When the amniotic sac breaks (“your water breaks”) before or during labor, these vessels can rupture and cause severe fetal bleeding and, in some cases, death. Fortunately, most (98%) cases of vasa previa are detected early in pregnancy, allowing the healthcare team to monitor the health of the fetus and plan for an early cesarean delivery to avoid these complications.  

  • When unprotected blood vessels lie over the cervix, there can be serious risks for the fetus. The fetus can receive less blood and oxygen if the blood vessels in the membranes are compressed. In addition, when the amniotic sac ruptures (when the water breaks), the fetal blood vessels in the membranes can tear, resulting in fetal bleeding. This can lead to severe fetal blood loss, anemia (low blood count), or even stillbirth. However, early detection and careful management can prevent complications and pregnancy loss in most cases. 

  • There are several risk factors for vasa previa:  

    • Velamentous cord insertion: In a velamentous cord insertion, the umbilical cord attaches to the fetal membranes instead of the placenta. This type of insertion leaves the fetal blood vessels exposed as they pass through the fetal membranes. The velamentous cord Insertion can be located away from the cervix (no risk of vasa previa) or close to the cervix (risk of vasa previa). 

    • Bilobed placenta: A bilobed placenta has two parts (lobes) connected by a thin band of tissue instead of just one lobe. If this thin band of tissue is near the cervix, this is a type of vasa previa.  

    • A low-lying placenta or placenta previa: A placenta that lies near or over the opening of the cervix also increases the risk of vasa previa. Sometimes, when a placenta previa resolves and moves upwards in the uterus, the fetal vessels remain near the cervix and become exposed in the fetal membranes, resulting in a vasa previa.  

    Pregnant people who had in vitro fertilization (IVF) or prior uterine surgery (eg, a cesarean delivery) or who have a multifetal pregnancy also have an increased risk of vasa previa. 

  • Vasa previa is typically detected by ultrasound imaging between 18 and 26 weeks of pregnancy. It is diagnosed if a fetal blood vessel is seen over or immediately next to the cervix. Detection later in pregnancy can be difficult.  

    If vasa previa is detected during your ultrasound exam, your healthcare professional will note where the placenta is in relation to the cervix, whether the placenta has more than 1 lobe, and the location of the umbilical cord insertion into the placenta. An ultrasound that measures blood flow through the vessels, called a Doppler ultrasound, may be performed to confirm the diagnosis. Typically, a transvaginal ultrasound is needed to best evaluate vasa previa. 

  • The goal is to prolong pregnancy as safely as possible while avoiding complications that can result when membranes rupture or labor occurs. Your pregnancy plan may include the following:  

    • Corticosteroids may be administered during pregnancy to help the fetal lungs and other organs develop in anticipation of a preterm delivery. 

    • You may need to stay in the hospital before your delivery to be monitored more closely. The timing of admission to the hospital is based on several different factors, including your medical history, the likelihood of going into preterm labor, and how far away you live from the hospital.  

    • A cesarean delivery will usually be scheduled between 34 and 37 weeks of pregnancy. You may need it sooner if other complications arise. 

    Your care will be individualized based on your unique risk factors, ultrasound findings, and specific clinical situation. Weekly fetal monitoring, called antenatal testing, may be recommended to closely monitor the fetus in the outpatient setting.  

  • If you have been diagnosed with vasa previa, a scheduled cesarean delivery is recommended between 34 and 37 weeks of pregnancy. Studies suggest that when vasa previa is diagnosed before delivery and early delivery is performed, the baby's survival rate is greater than 95%.  

    During the delivery, your healthcare professional may adjust the type of incision on your uterus depending on where the placenta and blood vessels are located. If one of the blood vessels tears during surgery, it will be quickly clamped to help minimize blood loss from your baby.  

    When planning a cesarean delivery, the goal is to balance the risks of an early delivery against the risk of labor or rupture of membranes and potential tearing of the vessels. The delivery should take place at a hospital capable of providing advanced care for your baby if needed, including an emergency blood transfusion. Babies who are born preterm may need specialized monitoring and treatment in the neonatal intensive care unit (NICU).  

  • Laser surgery to treat certain types of vasa previa may be an option in select cases. This type of surgery is performed at a fetal center.   

Quick Facts

  • Vasa previa is a rare but serious condition that occurs when fetal blood vessels that are unprotected by the umbilical cord or placenta run through the amniotic membranes and cross over the cervix. It can cause severe fetal bleeding if the membranes rupture before or during labor. 

  • Most cases of vasa previa are diagnosed during the second-trimester ultrasound given during pregnancy. Early diagnosis allows for monitoring and delivery planning that reduces the risk of pregnancy loss to less than 5%. 

  • Risk factors for vasa previa include velamentous cord insertion, bilobed placenta, a low-lying placenta or placenta previa, especially if resolved, in vitro fertilization, and previous uterine surgery. 

  • Management may include weekly outpatient fetal monitoring, corticosteroids to help fetal organs mature, possible in-hospital monitoring before you have your baby, and a scheduled cesarean delivery at 34 to 37 weeks of pregnancy.   

Glossary

Amniotic sac: The “bag of waters” that surrounds the fetus during pregnancy.  

Bilobed placenta: A placenta that has two lobes connected by a thin band of tissue.  

Cervix: The opening to the uterus located at the top of the vagina.  

Cesarean delivery: Surgery in which a baby is delivered through a cut (incision) in the mother’s uterus.  

Corticosteroids: Medication that can help a fetus’s lungs and other organs mature, usually given if a preterm delivery is anticipated. 

Fetus: During pregnancy, the stage of development from nine weeks to birth.  

In vitro fertilization (IVF): A procedure in which the egg and sperm are combined in a laboratory. The resulting embryo is transferred to the uterus a few days later or frozen for future transfer.  

Multifetal Pregnancy: Pregnancy with more than one fetus, such as twins, triplets, or more. 

Neonatal intensive care unit: A special unit in the hospital that cares for sick newborns. 

Placenta: A special organ that develops during pregnancy. It allows the transfer of nutrients, antibodies, and oxygen to the fetus. It also makes hormones that sustain the pregnancy.   

Placenta previa: A condition in which the placenta grows too low on the wall of the uterus and lies over the cervix. It can cause severe bleeding when the cervix begins to dilate (open) late in pregnancy.  

Stillbirth: Death of a fetus prior to delivery. 

Ultrasound: Use of sound waves to create images of internal organs or the fetus during pregnancy. 

Umbilical Cord: The structure linking the growing fetus to the placenta; it contains blood vessels that bring oxygen and nutrients to the fetus and remove waste products.  

Vasa previa: A condition in which fetal blood vessels that are unprotected by the umbilical cord or placenta run through the amniotic membranes and cross over the cervix. 

Velamentous cord insertion: Abnormal attachment of the umbilical cord to the placenta in which its blood vessels attach to the membranes surrounding the fetus. The exposed blood vessels can sometimes tear and bleed.  

 

Last Updated: October 2024