An extra placenta separate from the main placenta. Also called a succenturiate or supernumerary placenta. Placenta accreta: the abnormal adherence of the chorionic villi to the myometrium. The vascular processes of the chorion (a foetal membrane that enters into the formation of the placenta) grow directly in the myometrium (the muscular portion of the uterus). Normally there is tissue intervening between the chorionic villi and the myometrium. Here there is not. The word accreta comes from the latin accretio from ad meaning to or toward _ crescere meaning to grow. Placenta accreta can progress to placenta percreta.