Placenta accreta is an abnormal adherence of the placenta to the uterine wall. Three variants of abnormally invasive placentation have been described: placenta accreta, in which placental villi invade the surface of the myometrium; placenta increta, in which placental villi extend into the myometrium; and placenta percreta, where the villi penetrate through the myometrium to the uterine serosa and may invade adjacent organs, such as the bladder.