Placenta Previa: What It Means for Your Pregnancy

Medically Reviewed By Wendy A. Satmary, MD
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Placenta previa occurs when the placenta covers or lies close to the opening of the cervix during pregnancy. This can cause vaginal bleeding and contractions prior to labor. In nearly all cases, cesarean delivery is necessary, typically between 36–37 weeks of gestation. Placenta previa affects 0.3–2% of pregnancies in the third trimester. Certain types of placenta previa can cause serious and even life threatening complications.

When necessary, cesarean delivery and blood transfusions can reduce the risk of complications. However, people with placenta previa are at risk for hemorrhage before, during, and after delivery.

This article explains placenta previa, including symptoms and risk factors. It also discusses how doctors diagnose placenta previa and what it means for the rest of your pregnancy.

What is placenta previa?

The placenta is an organ that develops in the uterus during pregnancy. It coordinates with the umbilical cord to pass oxygen, glucose, and other nutrients to the fetus.

The cervix is the opening of the uterus that leads to the vagina. In vaginal deliveries, the baby passes from the uterus through the cervix into the vagina.

In a typical pregnancy, the placenta sits toward the top of the uterus, away from the cervix. With placenta previa, the placenta instead lies very low in the uterus and covers the opening of the cervix.

Medical illustration shows placenta previa vs placenta in the correct position
Placenta previa occurs when the placenta lies at the bottom of the uterus, blocking access to the cervix. Credit: BruceBlaus, CC BY-SA 4.0, via Wikimedia Commons

Because placenta previa blocks the path through the cervix, placenta previa requires cesarean delivery. Guidelines advise delivery around 36–37 weeks if there are no complications. However, if there is continued bleeding or risk to the pregnant parent or fetus, earlier delivery may be necessary.

What are the types of placenta previa?

There are two types of placenta previa, classified by the position of the placenta and the associated symptoms.

  • Complete previa: This type occurs when the placenta blocks the opening of the cervix completely. It typically causes severe bleeding and may prevent vaginal delivery.
  • Marginal previa: This type occurs when the edge of the placenta is within 2 centimeters (cm) of the opening of the cervix.

A separate but similar condition, low-lying placenta, occurs when the edge of the placenta is within 2–3.5 cm of the opening of the cervix. In 90% of cases of low-lying placenta, the bulk of the placenta naturally shifts away from the cervix before delivery.

Your doctor will review your individual diagnosis with you and discuss the safest options for your pregnancy and delivery.

What are the symptoms of placenta previa?

Overhead view of baby against mother's belly with visible C-section scar
Westend61/Getty Images

In many cases, placenta previa does not cause symptoms. Doctors may discover the condition on a routine prenatal ultrasound, such as the fetal anatomy scan. Obstetricians typically perform this scan between 16–20 weeks of gestation.

When symptoms do occur, they often include bright red vaginal bleeding, the most common symptom of placenta previa. This bleeding is usually painless and can range from light to heavy.

In some pregnant people, contractions may accompany the bleeding. Contractions may feel like a tightening of the belly or pressure in the back.

In cases where the bleeding is continuous or severe, symptoms of anemia may occur, including:

Contact your obstetrician or midwife if you have bleeding at any point in your pregnancy. 

What are the causes and risk factors for placenta previa?

It is unclear exactly what causes placenta previa. Some research has found that uterine scarring from other conditions or procedures could play a role.

Researchers have identified certain risk factors for placenta previa. However, not all people who have risk factors will develop placenta previa. Similarly, not all people who develop placenta previa have these risk factors.

Risk factors for placenta previa include:

  • previous cesarean delivery, which research has found to be a primary risk factor
  • previous pregnancy
  • previous pregnancy with placenta previa 
  • previous dilation and curettage procedure
  • pregnancy with two or more fetuses
  • conditions that affect the structure of the uterus, such as uterine fibroids
  • age 35 years and older
  • becoming pregnant with assisted reproductive technology
  • smoking
  • using cocaine

If you have risk factors and are pregnant or could become pregnant, talk with your obstetrician or midwife about steps to manage your risk.

How do doctors diagnose placenta previa?

Your obstetrician or midwife may diagnose placenta previa through a routine ultrasound as part of your prenatal care.

If you experience bleeding in the second or third trimester (weeks 13–40), your doctor or midwife may perform a transvaginal ultrasound. This can help rule out other possible causes of bleeding.

If the doctor diagnoses placenta previa, this test can also provide more detail about the location of the placenta.

Placenta accreta spectrum

If doctors diagnose placenta previa, they will likely also evaluate you for placenta accreta spectrum. This is a group of conditions in which the placenta grows too deeply into the uterine wall, sometimes extending into nearby pelvic tissue.

Placenta accreta spectrum is a more serious condition that may require urgent treatment.

What are treatments for placenta previa?

Treatment for placenta previa will depend on the type of previa you have and the symptoms you are experiencing. The gestation of your pregnancy will also influence the treatment options your obstetrician or midwife recommends.

Prior to 36 weeks

If you experience bleeding earlier than 34 weeks gestation and there may be a risk of premature delivery, doctors may give you corticosteroids. These medications help accelerate lung development in the fetus.

If you are not experiencing bleeding, your doctor may recommend watchful waiting to monitor your pregnancy. They may also recommend bed rest and advise you to avoid physical activities, such as sexual intercourse and exercise. 

If bleeding does occur earlier than 36 weeks gestation, but the birthing parent and fetus are stable, doctors may recommend hospitalization for closer monitoring.

If the first instance of bleeding stops, you may be able to go home and continue to avoid strenuous activity or sexual intercourse. If you experience a second bleeding episode, your obstetrician or midwife may recommend you stay in the hospital until you deliver.

Weeks 36–37

If the pregnant person and fetus are both stable, doctors will typically perform a cesarean delivery between weeks 36–37. The fetus’s lungs have developed enough to allow for safe delivery by this point in gestation.

Emergency delivery

If certain complications develop — regardless of the timing of gestation — doctors may need to perform an emergency cesarean delivery. Reasons for an emergency delivery include:

  • heavy or uncontrolled vaginal bleeding
  • concerning results from fetal heart monitoring
  • unstable blood pressure in the birthing parent

In some cases, the pregnant person may need a blood transfusion to replace blood lost through hemorrhaging. If there is severe or uncontrolled bleeding in the uterus, doctors may need to perform a hysterectomy following delivery to protect the life of the pregnant person.

When should you contact your doctor or midwife?

It is not uncommon to experience light bleeding or spotting in the first trimester.  If bleeding occurs in the second or third trimester, it could indicate a complication such as placenta previa.

Contact your obstetrician or midwife for any bleeding during your pregnancy or for any other symptoms that cause you concern.

Other frequently asked questions 

The following are other questions people have asked about placenta previa. Joshua Copel, MD, has reviewed the answers.

What is the risk of having placenta previa with a future pregnancy?

If you have placenta previa in one pregnancy, your risk of developing it in a future pregnancy is 2–3%. Having a cesarean delivery also increases your risk of placenta previa in future pregnancies. Talk with your obstetrician or midwife about your individual risk factors and step to help manage your risk.

Can an unborn baby survive placenta previa?

In most cases, placenta previa presents a greater threat to the life of the pregnant person than to the unborn baby. Doctors typically perform a cesarean delivery around weeks 36–37 of gestation. At this point, the fetus’s lungs have developed enough to allow for safe delivery. Doctors may need to perform a premature cesarean delivery in more serious cases, which puts the baby at higher risk for complications.

Is placenta previa a high risk pregnancy?

Placenta previa does increase the risk of complications during pregnancy and delivery. It typically requires cesarean delivery, which is a higher risk procedure than vaginal delivery. It also increases the risk of premature delivery.

Summary

Placenta previa occurs when the placenta blocks the opening of the cervix during pregnancy. Common symptoms include painless vaginal bleeding and contractions.

Most cases of placenta previa require a cesarean delivery. If complications develop earlier than 36 weeks, doctors may need to perform an emergency cesarean delivery to protect the life of the birthing parent and fetus.

Contact your obstetrician or midwife about any bleeding you experience during pregnancy or any other symptoms that cause you concern.

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Medical Reviewer: Wendy A. Satmary, MD
Last Review Date: 2022 May 31
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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