What it is. A condition, occurring in fewer than 1 percent of pregnancies, in which the placenta covers the cervix. This is dangerous because during labor, when the cervix dilates and the uterus expands, portions of the placenta may tear and bleed, causing the mother to hemorrhage.
What causes it. Doctors aren't sure, but risks include carrying multiple fetuses, having had C-sections or abortions, and being over 40.
Symptoms. Bleeding during the second or third trimester.
Treatment. If bleeding is light, your doctor may just monitor you closely. In 90 percent of cases, the placenta moves away from the cervix on its own. If the placenta completely blocks your cervix, however, your doctor may recommend bed rest. Recurrent bouts of bleeding may require hospitalization.
Can you prevent it? No. Simply report any bleeding to your doctor immediately.