What Is Placenta Previa?

Healthy pregnancies are still possible with placenta previa

Pregnant Hispanic woman touching her belly
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It can be alarming to get a diagnosis of placenta previa, a condition where the placenta sits low in the uterus, covering part or all of the cervix. Placenta previa is not associated with miscarriage or pregnancy loss, but it can cause severe bleeding and increase the risk of preterm birth and infant death. In most cases, however, it is detected early, managed well, and results in a healthy delivery.

Overview

In a normal pregnancy, the placenta—the organ that nourishes and protects the fetus—attaches to the upper part of the uterus where it doesn't cover the cervix, the opening to the vagina. In a case of placenta previa, the placenta attaches lower in the uterus where it can cover the cervical opening as it grows during the pregnancy.

There are three types of placenta previa:

  • Complete Previa: The cervix is completely covered.
  • Partial Previa: Only a portion of the cervix is covered.
  • Marginal Previa: The placenta only touches the edge of the cervix, but does not cover it.

Placenta previa can cause bleeding, particularly in the third trimester as your body begins to prepare for labor and the uterus thins. The amount of bleeding and the risks involved depend on how much of the cervix is covered and the degree of tearing it causes on the uterus.

According to the March of Dimes, placenta previa occurs in 1 in 200 pregnancies. It's much more common during the first 10 to 20 weeks of pregnancy, but most of these early cases—around 90 percent—resolve themselves by 32 to 35 weeks. Depending on where you are in your pregnancy, there's a good chance that your condition will correct itself before you give birth.

When the condition does not self-correct during pregnancy, a c-section may be necessary to prevent dangerous complications.

Causes

What causes placenta previa is unknown, but there are certain factors that can increase your risk:

  • Cigarette smoking
  • Cocaine use
  • Over the age of 35
  • Previous pregnancies
  • In vitro fertilization
  • Carrying more than one baby
  • Abnormal uterus shape
  • Previous surgery on your uterus (including c-section or D&C)
  • Placenta previa during a prior pregnancy

Symptoms

Bleeding after 20 weeks gestation is the most common symptom of placenta previa. Most women have painless bleeding, while a smaller number have either bleeding with uterine contractions or no bleeding.

Any bleeding in the second or third trimester of pregnancy should be reported to your physician without delay, whether or not you have placenta previa.

Diagnosis

Placenta previa can usually be detected during an ultrasound, through routine testing most practitioners perform around the 20th week of pregnancy. If you have not had ultrasounds during your pregnancy, the condition may be discovered when you start bleeding. 

Risks

Outcomes for babies from placenta previa pregnancies have been improving thanks to prenatal medical care. It does have the potential to slow fetal development and cause intrauterine growth restriction (IUGR), result in a breech baby, or cause health problems for the baby if delivery occurs too early.

Placenta previa does not cause miscarriage. However, in rare cases, placenta previa can lead to an infant's death during the first month of life. This is usually related to preterm birth, which is more common in placenta previa—although most babies are born at term. 

In the U.S., placenta previa is rarely fatal for the mother. If you do experience severe heavy bleeding, you may need a blood transfusion. 

Treatment

If you've been diagnosed with placenta previa, you may be advised to avoid intercourse or strenuous exercise to minimize bleeding. Your doctor may also advise bed rest and restrict travel if you are bleeding. The goal will be to delay delivery as long as possible so your baby can fully develop.

Your doctor will closely monitor you and the baby to ensure everything is going well. Women with placenta previa are sometimes hospitalized in the third trimester, in case they spontaneously go into labor, which could also cause severe bleeding. 

Early delivery by c-section will most likely be recommended if your placenta previa is still present in the third trimester. This may occur as soon as 34 to 36 weeks.

Your doctor may give you corticosteroids to boost your baby's lung maturity as well. Around 36 to 37 weeks, the amniotic fluid may be tested to see how lung development is progressing. If it's found to be in a good range, a c-section may be ordered at that time.

A Word From Verywell

Hearing that there is anything wrong with your pregnancy that might threaten your baby is understandably concerning. However, keep in mind that most women with placenta previa are able to carry their babies to term without serious complications. Follow your doctor's recommendations and be sure to ask any questions you may have.

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