Placenta previa is a placenta that has grown low in the uterus,
partially or fully over the opening to the birth canal (cervix). Placenta
previa can be dangerous during labor and delivery, when it is most likely to
cause severe placental bleeding that can be life-threatening to the mother or
fetus.
The amount of the cervix that is covered by the placenta may be
slight (marginal), moderate (partial), or complete (total). Unless a placenta
previa is only marginal, a surgical delivery (cesarean section) is needed to
prevent severe placental bleeding.
A woman's risk for placenta previa increases with each pregnancy,
cesarean section, uterine procedure that scars the uterus, or previous placenta
previa. Smoking, cocaine use, and advancing age also increase placenta previa
risk.
