Placenta Previa

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.

Looking for Placenta Previa Care?

On this page

• What Is Placenta Previa?
• What Are the Symptoms of Placenta Previa?  
• How Do You Diagnose Placenta Previa? 
• How Do You Treat Placenta Previa?

What Is Placenta Previa?

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.

What are the types of placenta previa?

There are two types of placenta previa:

• Partial previa — When the placenta partially blocks the cervix.
• Complete previa — When the placenta fully covers the cervix.

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.

What causes placenta previa?

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.

Placenta previa risk factors and complications

Placenta previa risk factors

Certain risk factors increase your chances of developing placenta previa.

These include:

• Age — Being older than 35 during pregnancy.
• Multiples — Being pregnant with twins, triplets, or more can impact where the placenta implants.
• Multigravida — Having been pregnant before.
• Assisted reproduction – Having had IVF can increase risk.
• A history of placenta previa — If you've had placenta previa in the past, there is a 2 to 3% chance you could have it again, according to the March of Dimes.
• Uterine scarring – A previous C-section or other surgery on the uterus, such as uterine fibroid removal or dilation and curettage after a miscarriage, could leave scarring.
• Smoking — The nicotine and carbon monoxide in cigarettes compromise blood flow to the placenta, affecting its development. 
• Substance abuse — Especially the use of cocaine or crack.

Placenta previa complications

Placenta previa can cause a variety of complications during pregnancy:

• Developing placenta accreta spectrum disorder, a serious pregnancy condition in which the placenta grows too deeply into the wall of the uterus.
• Severe vaginal bleeding. In cases of extreme blood loss, you may need a blood transfusion.

Placenta previa can cause a variety of complications during delivery, including:

• C-section delivery.
• Hysterectomy, or removal of the uterus, which renders a person incapable of becoming pregnant again. You may need a hysterectomy if bleeding does not stop after delivery.
• Hospitalization or admission to the intensive care unit (ICU).
• Maternal death.
• Postpartum hemorrhage, or the loss of blood from a damaged blood vessel within 24 hours after delivery.
• Sepsis is an aberrant reaction to an infection.

Placenta previa can also harm the baby. Complications that impact the baby include:

• A low birth weight baby.
• Lower APGAR scores in your baby (a rating of your baby's color, heart rate, muscle tone, reflexes, and breathing.)
• Stillbirth, or fetal death.
• Preterm delivery, which can lead to a variety of complications with your baby's health.
• Risk of respiratory distress syndrome in your baby if your baby's lungs haven't fully formed before delivery. Your doctor will give you medicine to develop your baby's lungs to reduce this risk.
• Vasa previa, or a condition when blood vessels from the umbilical cord or placenta cross the cervix and can be torn during labor. While rare, the bleeding that can result in your baby due to vasa placenta can be life-threatening.

Can you prevent placenta previa?

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:

• Having an orgasm.
• Lifting anything 20 pounds or heavier.
• Moderate to intense physical exercise.
• Smoking.
• Standing for more than four hours a day.
• Using cocaine or crack.
• Vaginal examinations.
• Vaginal penetration.

Back to top

What Are the Symptoms of Placenta Previa?  

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.

Back to top

How Do You Diagnose Placenta Previa? 

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:

• 3D ultrasound.
• Transvaginal ultrasound using a wand through the vagina to help determine the location of the placenta and look at your cervix.
• Doppler ultrasound to see blood flow in the placenta.

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.

Back to top

How Do You Treat Placenta Previa?

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:

• How much you are bleeding.
• Your baby's gestational age.
• The position and location of your placenta.
• The position of your baby.
• The health of you and your baby.

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:

• Avoiding certain activities like sexual intercourse and exercise.
• Avoiding vaginal examinations to reduce the risk of disturbing your placenta and causing bleeding.
• Reduced activity and bed rest.
• Blood transfusion in the event of significant bleeding.
• Planned C-section delivery at 36 or 37 weeks.
• If you develop severe bleeding between 34 and 36 weeks, you may need an emergency C-section. 
• Hysterectomy if you're bleeding too much after birth.
• Longer hospitalization before and after delivery.
• Medication to decrease the risk of your baby having breathing difficulties or prevent premature labor.
• Medication to treat anemia or a lack of red blood cells in your blood.
• Monitoring for bleeding and preterm labor.

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.

By UPMC Editorial Staff. Last reviewed on 2024-09-05.