Placenta previa

Definition

Placenta previa is a rare condition in which the placenta grows in the lower part of a pregnant woman's uterus and covers all or part of the cervix.

The placenta is the organ that nourishes the developing fetus.

Causes, incidence, and risk factors

Possible causes of placenta previa include:

• Abnormal formation of the placenta
• Abnormal uterus
• Large placenta
• Scarred lining of the uterus (endometrium)

Placenta previa is very rare. The risk increases with each pregnancy, especially in women who have had six or more deliveries. The rate of placenta previa is also higher in women who are carrying more than one baby (multiple pregnancy).

Risk factors include:

• Multiple pregnancy
• Previous deliveries (multiparity)
• Previous C-section (if the scar is low and close to the vaginal cervix region)
• Previous removal of uterine fibroids through a surgical cut in the uterus (myomectomy)
• Smoking

Symptoms

• Spotting during the first and second trimesters of pregnancy
• Sudden, painless, and heavy vaginal bleeding in pregnancy during the third trimester (usually after 28 weeks)
• Uterine cramping with the bleeding

Note: Bleeding may not occur until after labor starts in some cases. Labor sometimes starts within several days after heavy vaginal bleeding.

Signs and tests

The uterus is usually soft and relaxed. In a small number of cases, the infant is in an unusual position. Fetal distress doesn't usually occur unless there is a cord accident, or vaginal blood loss has been heavy enough to cause placenta abruptio or shock in the mother.

An abdominal ultrasound during the second trimester can show whether the placenta is low. Transvaginal or transperineal ultrasound can help the doctor see the position of a low-lying placenta.

Treatment

Treatment depends on the amount of abnormal uterine bleeding, whether the fetus is developed enough to survive outside the uterus, the amount of placenta over the cervix, the position of the fetus, the number of previous births (parity) for the mother, and whether the mother is in labor.

Early in pregnancy, transfusions may be given to replace blood the mother has lost. The mother may get medications to prevent premature labor, and continue the pregnancy to at least 36 weeks. Beyond 36 weeks, the benefits of the infant maturing have to be weighed against the possibility of a major hemorrhage.

Cesarean section is the delivery method for placenta previa. It is the most important way to reduce mother and infant death rates.

Expectations (prognosis)

The outcome is excellent when the condition is managed properly. This means hospitalizing a mother who is having symptoms, and delivering by C-section.

Complications

Risks to the mother include:

• Death
• Major bleeding (hemorrhage)
• Shock

The risks of infection and blood clots (thromboembolism) also increase, as does the likelihood that the mother will need a blood transfusion.

Prematurity (infant is less than 36 weeks gestation) causes most infant deaths in cases of placenta previa. Fetal blood loss or hemorrhage may occur because the placenta separates from the wall of the uterus during labor. The fetus also can lose blood when the uterus is opened during a C-section delivery.

Calling your health care provider

Call your health care provider if you have bleeding from the vagina at any point in your pregnancy. Placenta previa can be dangerous to both you and your baby.

Prevention

This condition is not preventable.