Deep placentation in the human requires physiologic transformation of the spiral arteries
into uteroplacental vessels. This process involves the inner myometrial segment (junctional
zone) of the spiral arteries and is effected by trophoblast invasion of the vessel wall,
resulting in complete loss of the arterial structure and deposition of fibrinoid and fibrous
tissues. Absent or inadequate physiologic changes in the junctional zone spiral arteries
limits placental blood flow in pregnancies complicated by preeclampsia and fetal growth …