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Placenta Previa - Topic Overview

What is placenta previa?

Placenta previa is a pregnancy problem in which the placenta blocks the cervix. The placenta is a round, flat organ that forms on the inside wall of the uterus soon after conception. During pregnancy, it gives the baby food and oxygen from the mother.

In a normal pregnancy, the placenta is attached high up in the uterus, away from the cervix. In placenta previa, the placenta forms low in the uterus camera.gif and covers all or part of the cervix.

If placenta previa is present during labor and delivery, it can cause problems for both mother and baby.

  • The mother may lose a lot of blood, which can be dangerous for both her and her baby.
  • The placenta may separate too early from the wall of the uterus. This is called placenta abruptio, and it can cause serious bleeding, too.
  • The baby may be born too early (premature), at a low birth weight, or with a birth defect.

What causes placenta previa?

Doctors aren't sure what causes this problem. But some things make you more likely to have it. These are called risk factors.

You can't control most risk factors for placenta previa. For example, you're more likely to have it if you:

  • Have had a surgery that affected your uterus, such as a D&C or surgery to remove uterine fibroids (myomectomy).
  • Have had a previous C-section (cesarean delivery).
  • Have had five or more pregnancies.
  • Are age 35 or older.
  • Have had placenta previa before.

Risk factors you can control include:

What are the symptoms?

Some women with placenta previa don't have any symptoms. But others may have warning signs such as:

  • Sudden, painless vaginal bleeding. The blood is often bright red, and the bleeding can range from light to heavy.
  • Symptoms of early labor. These include regular contractions and aches or pains in your lower back or belly.

Call your doctor or go to the nearest emergency room right away if you have:

How is placenta previa diagnosed?

Most cases of placenta previa are found during the second trimester when a woman has a routine ultrasound. Or it may be found when a pregnant woman has vaginal bleeding and gets an ultrasound to find out what is causing it. Some women don't find out that they have placenta previa until they have bleeding at the start of labor.

A pelvic exam will not be done unless you need a C-section right away. A pelvic exam could injure the placenta and cause heavier bleeding.

How is it treated?

The kind of treatment you will have depends on:

  • Whether or how much you are bleeding.
  • How the problem is affecting your health and your baby's health.
  • How close you are to your due date.
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