Placenta previa is a serious pregnancy complication. It occurs when the placenta partially or completely blocks the opening of your cervix. It can cause life-threatening bleeding during pregnancy and delivery.
Placenta previa occurs in about 1 in 200 pregnancies, according to the National Library of Medicine. Most people with placenta previa must deliver their baby by C-section. If the placenta doesn't move by the third trimester, the pregnancy is high-risk.
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Placenta previa occurs when the placenta partially or completely covers the entrance to the birth canal. The entrance to the birth canal is also called the opening of your cervix. It's what opens during labor and how the baby exits the body during a vaginal delivery.
The placenta is a round, flat organ that forms during pregnancy. It provides food and oxygen to your baby through the umbilical cord. In most pregnancies, the placenta attaches near the top or side of the uterine wall.
But if you have placenta previa, the placenta attaches near the bottom of your uterus. It can fully or partially block the opening of your cervix.
It's normal for the placenta to lie near the cervix early in pregnancy. A low-lying placenta doesn't block the cervix but is within two centimeters of the opening. As your baby grows, the placenta moves higher. About 90% of low-lying placentas will resolve naturally by the third trimester of pregnancy, according to StatPearls.
If the placenta previa fixes itself by moving out of the way, you can have a normal delivery with placenta previa.
But when placenta previa persists into the third trimester, the pregnancy is considered high-risk. Placenta previa occurs in 0.3% to 2% of third-trimester pregnancies, according to StatPearls.
With the placenta in this position, a vaginal delivery poses a higher risk risk of severe bleeding. It can also cause bleeding during pregnancy. To avoid bleeding during vaginal delivery, your doctor may recommend a planned cesarean delivery (C-section) to avoid going into labor.
There are two types of placenta previa:
As you near your due date, your cervix thins and opens so your baby can pass through. If the placenta is too close to the cervix, blood vessels attached to it can tear. Any type of placenta previa can cause heavy bleeding in your third trimester or when you're in labor.
The exact cause of placenta previa is unknown. It might be due to uterine scarring or damage to the endometrium (uterine lining) from surgery, including prior C-sections. Placenta previa seems more common as the C-section rate has increased in recent decades.
Certain risk factors increase your chances of developing placenta previa.
These include:
Placenta previa can cause a variety of complications during pregnancy:
Placenta previa can cause a variety of complications during delivery, including:
Placenta previa can also harm the baby. Complications that impact the baby include:
While you can't prevent this condition, you and your provider can manage it. Keep your blood levels high throughout pregnancy, having a plan for heavy bleeding during delivery.
You can help reduce the risk of bleeding during your pregnancy. Your doctor may tell you to avoid the following activities.
These may trigger contractions that could lead to bleeding:
The main symptom of placenta previa is painless, bright red vaginal bleeding that occurs during the second or third trimester of your pregnancy. Sometimes, the bleeding stops without treatment and may start again within a few days or weeks. Some people with bleeding from placenta previa may experience cramps.
Bleeding can range from light to heavy, and you may experience contractions. Any episodes of vaginal bleeding, no matter how minor they may seem, should be reported to your doctor immediately. If you have severe vaginal bleeding, you should go to the nearest hospital right away.
About one-third of people with placenta previa do not have vaginal bleeding, according to the March of Dimes.
Heavy vaginal bleeding in the third trimester can also be caused by a placental abruption, in which the placenta starts to detach from the uterus. It is possible to have placenta previa and also develop a placental abruption.
The most common way doctors find placenta previa is with a normal ultrasound. Your doctor may perform other types of ultrasounds to confirm placenta previa.
These may include:
Your doctor may also order a blood test to check your blood count or determine your blood type if you need a transfusion during delivery.
You'll have more ultrasounds to check on the placenta during your second trimester. If the placenta is not covering your cervix, you may still be able to deliver vaginally.
Depending on how far along you are, the doctor will likely watch and wait to see if the placenta moves on its own. They will continue to assess your condition and consider many factors before choosing a course of treatment.
They look at:
The goal of managing placenta previa is for you to carry your pregnancy as far to term as possible. But if you are experiencing severe or continuous bleeding, you may need a C-section regardless of gestational age. Your care team will help you to weigh the risk of bleeding against the risk of delivering your baby early.
Depending on your condition and the health of your baby, your doctor may suggest:
If you are not bleeding and make it to 36 or 37 weeks, your doctor may conduct an amniocentesis. This amniotic fluid test can check your baby's lung development. If they are, you may deliver early via a C-section.
Last reviewed by a UPMC medical professional on 2024-09-05.
