Placenta accreta refers to an abnormality of placental implantation in which the anchoring placental villi attach to myometrium rather than decidua, resulting in a morbidly adherent placenta. Placenta increta (chorionic villi penetrate into the myometrium) and placenta percreta (chorionic villi penetrate through the myometrium to the uterine serosa or adjacent organs) are related, but more severe, abnormalities of placental implantation. The pathogenesis is primarily attributed to defective decidualization of the implantation site .
Unless otherwise noted, the following discussion of placenta accreta applies to all depths of placental invasion.
Placenta accreta is much more common than placenta increta and percreta. In a pooled analysis of results from two series involving a total of 138 histologically confirmed, abnormally implanted placentas from hysterectomy specimens, the type and frequency of abnormal placentation were [2,3]:
●Placenta accreta: 79 percent
●Placenta increta: 14 percent