Original Article: http://www.mayoclinic.com/health/medical/IM00579
The placenta is a structure that develops in the uterus during pregnancy. In most pregnancies, the placenta is located at the top or side of the uterus. In placenta previa, the placenta is located low in the uterus. The placenta might partially or completely cover the cervix, as shown here. Placenta previa can cause severe bleeding in the mother before or during delivery. A C-section delivery might be required.