Placenta creta and placenta praevia creta.

The placental bed in placenta creta and placenta praevia creta was studied from pregnancy or immediate postpartum hysterectomy specimens. In all cases placental villi were seen in direct contact with myometrium, the sine qua non of placenta creta, but was focal in some cases. There was no apparent diminution of decidua parietalis or, in cases of focal accreta, of adjacent basalis. In all cases the extravillous trophoblast was mainly uninuclear or binuclear, in contrast to the placental bed syncytial giant cells seen in late normal placentation. There was an apparent proliferation of interstitial trophoblast at the junction of placenta with myometrium, but the density of interstitial trophoblast deeper in the myometrium was lower than it is in normal placentation. An unusual uteroplacental vasculature was seen in which physiological changes were present in large arteries of the radial/arcuate system deep in the myometrium, while there were also spiral arteries more superficially without physiological changes. These findings suggest that in placenta creta there is defective interaction between maternal tissues, particularly decidua, and migratory trophoblast in the early stages of placentation resulting in undue adherence of the placenta or penetration into the uterus coupled with the development of an abnormal uteroplacental circulation.