We don't know definitively what causes placenta accreta. For some reason the villi that surround the placenta reach into the uterine wall deeper than they need to when they attach the placenta. Because of this, the placenta has difficulty detaching from the uterus after delivery.
During pregnancy, the placenta attaches to the surface of the uterine wall, however sometimes the placenta attaches itself too deeply into the wall of the uterus, and is a condition called placenta accreta. Placenta is attached deep in the uterine wall. As a result of this deep attachment, the placenta does not spontaneously separate during the third stage of labor. The cause of a placenta accreta is unknown, but risk factors include events that change the integrity of the uterine surface such as: pervious cesarean birth or uterine surgery, previous d & c, placenta previa, and grand, multiparity.
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