Abnormally invasive placenta (AIP) is a clinical term used to describe a placenta that does not separate spontaneously at delivery and cannot be removed without causing abnormally high blood loss. It encompasses the histopathological diagnoses of placenta accreta, placenta increta and placenta percreta.
It is a spectrum disorder, ranging from placentae containing a small area of abnormally adherent tissue (focal accreta) to those which have invaded into the adjacent viscera (percreta). It is potentially life-threatening, as forced removal of an AIP can lead to catastrophic maternal hemorrhage.