Figure 4.

Spiral artery remodeling in normal and abnormal placentation. During normal placentation, EVT cells invade uterine wall and maternal spiral arteries replacing smooth muscle with fibrinoid material and part of vessel endothelium, thus evoking artery dilatation. Decidual immune cells, like macrophages and NK cells, facilitate deep invasion of EVT cells up to myometrial portions of spiral arteries. A limited EVT cell invasion, in abnormal placentation, impairs the formation of the high-capacity, low-resistance feto-maternal circulation needed for an adequate oxygen and nutrient supply for the growing fetus. For cell type description, see figure 2.