Fig. 1.

Schematic diagram of spiral uterine artery remodelling by trophoblasts and in vitro assays used to model different stages in this process. Chorionic villi sprouting from the blastocyst consist of two distinct villous trophoblast cell types: syncytiotrophoblasts and cytotrophoblasts. The syncytiotrophoblasts forms the outer layer of the chorionic villi, whereas cytotrophoblast layer is considered stem like. Column trophoblasts are found in the anchoring villi where they form partially complete shell facilitating movement of extravillous trophoblasts through the maternal decidua (migration). Interstitial trophoblasts, upon entering decidua, gather and destroy arterial media (invasion); endothelial cells undergo apoptosis, which allows for their replacement by endovascular trophoblasts (co-culture). The most commonly found lymphocytes in the decidua during pregnancy are natural killer (NK) cells (co-culture)