When the placenta is attached closer to the bottom of the uterus than it should be, this is called placenta previa. In this position, the placenta either partially or completely blocks the opening in the cervix. Depending on the extent of the condition, it can put the mother and baby at risk if a vaginal delivery is attempted.
Normally, the placenta is attached to the inside wall of the uterus, either up along the side or the top of it. Placenta previa occurs when the placenta is attached closer to the bottom and either partially or completely blocks the opening in the cervix. This happens in about 1 out of every 200 pregnancies. The most common symptom of placenta previa is painless bleeding in the later stages of pregnancy.
When placenta previa is diagnosed earlier in the pregnancy (which is possible using ultrasound), it is monitored very closely. In cases where the placenta partially covers the cervix early in the pregnancy, it's possible for the placenta to move away from the cervix as the pregnancy progresses. If a partial placenta previa still exists when true labor begins, a vaginal delivery may be possible. However, in cases where the placenta covers the entire cervix, a cesarean delivery is usually recommended.
Why does placenta previa become serious if a normal vaginal delivery is attempted? With this condition, as the cervix dilates, it usually causes the placenta to separate from the wall of the uterus too early. This can result in serious bleeding that can be fatal for both the mother and the baby. Because of this, cesarean delivery is usually recommended in such cases.