Placenta Previa

Medically Reviewed by Traci C. Johnson, MD on November 12, 2022
3 min read

Placenta previa is when a pregnant woman's placenta blocks the opening to the cervix that allows the baby to be born. It can cause severe bleeding during pregnancy and delivery. Mothers with placenta previa are also at higher risk of delivering prematurely, before 37 weeks of pregnancy.

The placenta is an organ that grows inside the lining of your uterus during pregnancy. It connects to the umbilical cord and carries oxygen and nutrients from you to your unborn child. It also moves waste away from your baby.

Placenta previa happens when the placenta partly or completely covers the cervix, which is the opening of the uterus. Your baby passes into the cervix and through the birth canal during a vaginal delivery. Normally, the placenta does not attach near the cervix.

Here's what happens with placenta previa: As your cervix opens during labor, it can cause blood vessels that connect the placenta to the uterus to tear. This can lead to bleeding and put both you and your baby at risk. Women who have this condition will have to have a C-section to keep this from happening.

Types of placenta previa

You may have different outcomes depending on the type of placenta previa you have.

  • Complete previa is when the placenta covers the entire opening of the cervix.
  • Marginal previa, also called low-lying placenta, is when the placenta is close to the opening of the cervix but doesn't cover it. It may get better on its own before the baby is due.

You might notice:

  • Bright red bleeding from the vagina during the second half of your pregnancy. It can range from light to heavy, and it's often painless.
  • Contractions along with the bleeding. You might feel the cramping or tightening that comes with contractions, or feel pressure in your back.

If you have bled too much, you may have other symptoms, such as anemia, pale skin, rapid and weak pulse, shortness of breath, or low blood pressure.

Placenta previa happens in about 1 out of every 200 pregnancies. You may be more likely to get it if you:

  • Smoke cigarettes or use cocaine
  • Are 35 or older
  • Have been pregnant before
  • Have had a C-section before
  • Have had other types of surgery on your uterus
  • Are pregnant with more than one baby
  • Are a person of color

Doctors often diagnose placenta previa during an ultrasound on one of your routine prenatal visits. The test uses sound waves to show if your placenta covers the opening from your womb to your cervix. They'll start with a device called a transducer placed on your abdomen, but if they need a better look they'll use a transducer that goes inside your vagina. 

There's no cure for placenta previa. The goal of treatment is to limit the bleeding so you can get as close as possible to your due date.

Your doctor could give you medicine to prevent premature labor. They may also give you corticosteroid shots to help your baby’s lungs develop faster. Once they feel that the baby can be safely delivered (by about 36 weeks of pregnancy), they’ll schedule a C-section. If your bleeding won’t stop, you’ll need an emergency C-section, even if your baby is not full term.

Treatment depends on:

  • The amount of bleeding. If it's light, your doctor might suggest you avoid activities including sex and exercise. If it's heavy, you may need to go to the emergency room, stay in the hospital, and get a blood transfusion.
  • How close you are to your due date
  • Your health and your baby's health
  • The position of the placenta and the baby

Check with your doctor if you have bleeding during your second or third trimester. If it's severe, go to the hospital.