Abnormally invasive placenta (AIP) renders normal placental delivery impossible and carries a high risk for severe hemorrhage. AIP is associated with a significant increased maternal morbidity and a reported maternal mortality up to 7%.
Histopathologically, there are three degrees of abnormally deep placental invasion: placenta accreta, increta and percreta. All cases with AIP can be referred to as “placenta accreta”; but clinically, two main groups should be differentiated based on the extent of invasion: “simple placenta accreta” with abnormally adherent placenta that requires manual removal or curettage, but no further surgical procedures to achieve hemostasis and to restore normal uterine tone (such cases were not included in our study); and the more relevant group of AIP comprising cases with invasion of the uterus only (placenta increta; or placenta percreta with extension limited to the uterine serosa) and AIP with extra-uterine invasion (bladder, bowel, other internal organs).
In cases with the clinical diagnosis of “ simple placenta accreta” pathological confirmation is usually not available. The reported incidence of abnormally deep placental infiltration varies between 1/1000 and 1/2500 deliveries, but has increased ten times over the last 50 years, probably as a consequence of rising rate of cesarean deliveries. Further risk factors include placenta previa, other previous uterine surgery, multiparity, advanced maternal age, Asherman’s syndrome and submucous myoma. In the presence of placenta previa the risk of “placenta accreta” increases from 24% in a patient with a history of one previous cesarean delivery to 67% in a patient with a history of three or more cesarean deliveries. Combined results from two series using the three-stage definition, comprising a total of 138 histologically confirmed AIPs from hysterectomy specimens, the distribution of stages was 79% placenta accreta, 14% placenta increta and 7% placenta percreta.
Clinical problems occur mostly during the third trimester and delivery, but uterine rupture due to placenta increta/percreta can occur also early in gestation from 14 weeks onwards.