Defective deep placentation.

Defective deep placentation is characterised by defective remodelling of the utero-placental arteries. Under certain conditions, it is also characterised by the presence of arterial lesions, such as acute atherosis and the persistence of endovascular trophoblast. The condition has been associated with a spectrum of complications during pregnancy, including pre-eclampsia, intrauterine growth restriction, pre-term birth, pre-term premature rupture of membranes, late sporadic miscarriage and abruptio placentae. Criteria are proposed for the classification of defective deep placentation into three types based on the degree of restriction of remodelling and the presence of obstructive lesions in the myometrial segment of the spiral arteries. Although the underlying mechanisms are not understood, evidence is emerging that the origin of defective deep placentation may not lie in primary defect of the trophoblast, but in abnormalities of the endometrium and inner myometrium before or during the early stages of placentation.