During pregnancy, the placenta attaches to the wall of the uterus and supplies the baby with food and oxygen through the umbilical cord. Placenta previa is a condition in which the placenta lies very low in the uterus and covers all or part of the cervix. (The cervix is the opening to the uterus that sits at the top of the vagina.)
Placenta previa happens in about 1 in 200 pregnancies. If you have placenta previa early in pregnancy, it usually isn’t a problem. It will be monitored, however, because it can cause serious bleeding and other complications later in pregnancy.
Normally, the placenta grows into the upper part of the uterus wall, away from the cervix. It stays there until your baby is born. During the last stage of labor, the placenta separates from the wall, and your contractions help push it into the vagina (birth canal). This is also called the afterbirth.
During labor, your baby passes through the cervix into the birth canal. If you have placenta previa, when the cervix begins to efface (thin out) and dilate (open up) for labor, blood vessels connecting the placenta to the uterus may tear. This can cause severe bleeding during labor and birth, putting you and your baby in danger.
The most common symptom of placenta previa is painless bleeding from the vagina during the second half of pregnancy. Call your health care provider right away if you have vaginal bleeding anytime during your pregnancy. If the bleeding is severe, go to the hospital.
An ultrasound usually can find placenta previa and pinpoint the placenta’s location. In some cases, your provider may use a transvaginal ultrasound instead.
Even if you don’t have vaginal bleeding, a routine, second trimester ultrasound may show that you have placenta previa. Don’t be too worried if this happens. Placenta previa found in the second trimester fixes itself in most cases.
Treatment depends on how far along you are in your pregnancy, the seriousness of your bleeding and the health of you and your baby. To learn more, read our article on placenta previa.