Placenta previa is an uncommon condition affecting pregnant women. It occurs when the placenta, the vital organ that provides oxygen and nutrients to the growing baby and removes waste products from the baby's blood, partially or totally covers the woman's cervix. If a woman goes into labor with placenta previa, the placenta can detach from the uterus wall and cause excessive vaginal bleeding. As a result, most women with placenta previa deliver their baby by cesarean section. Follow the links below to find WebMD's comprehensive coverage about placenta previa, what it looks like, how to treat it, and much more.