Placenta previa

Placenta previa is the placement of the baby's placenta over the cervical os of the mother. Placenta previa is a life-threatening condition that can cause hemmorhaging in the mother as the cervix dilates and opens during labor, also causing a loss of blood and oxygen to the baby.

If caught before labor, a cesarean is normally scheduled in order to protect the mother and baby from the probably hemmorhage.

There are varying degrees of placenta previa, including complete, marginal, or "low-lying" placenta, meaning that the placenta is close to the os but not actually on it.