Placenta previa

Placenta previa (pluh-SEN-tuh PREH-vee-uh) occurs when a baby's placenta partially or totally covers the opening in the mother's cervix — the lower end of the uterus that connects to the top of the vagina. Placenta previa can cause severe bleeding before or during delivery.

The placenta provides oxygen and nutrients to your growing baby and removes waste products from your baby's blood. It attaches to the wall of your uterus, and your baby's umbilical cord arises from it. In most pregnancies, the placenta attaches at the top or side of the uterus. In placenta previa, the placenta attaches to the lower area of the uterus.

If you have placenta previa, you'll probably be restricted from physical exertion for a portion of your pregnancy and you'll likely require a cesarean section (C-section) to safely deliver your baby.

Symptoms Causes Risk factors Complications

Bright red vaginal bleeding without pain during the second half of pregnancy is the main sign of placenta previa. Bleeding ranges from light to heavy. The bleeding usually stops without treatment, but it nearly always returns days or weeks later. Some women also experience contractions.

When to see a doctor

If you have vaginal bleeding during your second or third trimester, call your doctor right away. If the bleeding is severe, seek emergency medical care.

The placenta grows wherever the embryo implants itself in the uterus. If the embryo implants itself in the lower portion of the uterus, the placenta might grow over the cervix — causing placenta previa.

Most cases of placenta previa are diagnosed during a second trimester ultrasound examination. If the placenta just barely reaches the cervix, expansion of the uterus may pull the placental attachment higher, away from the cervix, which will resolve the situation.

If the placenta is across the cervix, however, it's unlikely to resolve with time. The later in pregnancy that placenta previa exists, the more likely it will be present at the time of delivery.

Persistent types of placenta previa have been associated with:

  • Scars in the lining of the uterus, such as from previous surgery
  • A large placenta, such as with a multiple pregnancy
  • Being 35 or older during pregnancy
  • Having had babies

Women are at higher risk for placenta previa if they've had previous surgeries involving the uterus, such as:

  • A C-section
  • Surgery to remove uterine fibroids
  • Dilation and curettage, though this presents a much lower risk

Placenta previa is also more common among women who:

  • Have delivered at least one baby
  • Had placenta previa with a previous pregnancy
  • Are carrying more than one fetus
  • Are age 35 or older
  • Are of a race other than white
  • Smoke
  • Use cocaine

If you have placenta previa, your health care provider will monitor you and your baby to reduce the risk of these serious complications:

  • Bleeding. Severe, possibly life-threatening vaginal bleeding (hemorrhage) can occur during labor, delivery or the first few hours after delivery.
  • Preterm birth. Severe bleeding may prompt an emergency C-section before your baby is full term.
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