Written by WebMD Editorial Contributors Reviewed by Arefa Cassoobhoy, MD, MPH on July 28, 2020 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 attaches toward the top of the uterus, away from 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. Nearly all 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. You might notice: 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
Make an appointment if you have bleeding during your second or third trimester. If it's severe, go to the hospital.
ABOUT CAUSES DIAGNOSIS TREATMENT NEXT STEPS
Bleeding can happen at any time during pregnancy. Placenta previa can cause bleeding late in pregnancy. This means after about 20 weeks.
When the placenta is attached close to the opening of the uterus (cervix) or covers the cervix, it is called placenta previa. There are 3 types of placenta previa:
- Complete placenta previa. The placenta completely covers the cervix.
- Partial placenta previa. The placenta is partly over the cervix.
- Marginal placenta previa. The placenta is near the edge of the cervix.
Researchers don't know what causes placenta previa. It is more likely to happen with certain conditions. These include:
- Past pregnancies
- Tumors (fibroids) in the uterus. These are not cancer.
- Past uterine surgeries or cesarean deliveries
- Woman who is older than 35
- Woman who is African American or of another nonwhite ethnic background
- Cigarette smoking
- Placenta previa in a past pregnancy
- Being pregnant with a boy
The most common symptom of placenta previa is bright red, painless bleeding from the vagina. This is most common in the third trimester of pregnancy.
The symptoms of placenta previa may look like other health conditions. Make sure to see your healthcare provider for a diagnosis.
Your healthcare provider will ask about your health history. He or she will do a physical exam. The provider will also do an ultrasound. An ultrasound uses sound waves to make a picture of the organs. It can show where the placenta is and how much is covering the cervix. You may have a transvaginal ultrasound instead.
An ultrasound may show that a placenta is near the cervix in early pregnancy. But only a few women will develop true placenta previa. It is common for the placenta to move away from the cervix as the uterus grows.
There is no treatment to change the position of the placenta. You may need:
- More ultrasounds to track where the placenta is
- Bed rest or hospital stay
- Early delivery of the baby. This will be based on how much bleeding you have, how far along your baby is, and how healthy the baby is.
- Cesarean section delivery
- Blood transfusion for severe blood loss
The greatest risk of placenta previa is too much bleeding (hemorrhage). Bleeding often happens as the lower part of the uterus thins during the third trimester of pregnancy. This causes the area of the placenta over the cervix to bleed. The risk of bleeding is higher if a lot of the placenta covers the cervix. Other complications include:
- Placenta doesn't attach to the uterus as it should
- Slowed growth of your baby in the uterus
- Preterm birth (before 37 weeks of pregnancy)
- Birth defects
Call your healthcare provider about any bleeding you have while pregnant. Bleeding during pregnancy may not be serious. If the bleeding is moderate to severe, or you have pain, contact your healthcare provider right away.
Key points about placenta previa
- Placenta previa is a cause of bleeding late in pregnancy. This is after about 20 weeks.
- It causes bleeding because the placenta is close to or covers the cervix.
- Bleeding with placenta previa is painless.
- You may need bed rest or early delivery of your baby.
Tips to help you get the most from a visit to your healthcare provider:
- Know the reason for your visit and what you want to happen.
- Before your visit, write down questions you want answered.
- Bring someone with you to help you ask questions and remember what your provider tells you.
- At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.
- Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
- Ask if your condition can be treated in other ways.
- Know why a test or procedure is recommended and what the results could mean.
- Know what to expect if you do not take the medicine or have the test or procedure.
- If you have a follow-up appointment, write down the date, time, and purpose for that visit.
- Know how you can contact your provider if you have questions.
Medical Reviewer: Daniel N Sacks MD
Medical Reviewer: Donna Freeborn PhD CNM FNP
Medical Reviewer: Heather Trevino
© 2000-2022 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.