cytotrophoblast

Cytotrophoblasts are mononucleated, epithelial-like cells that form the inner cellular layer of the placental trophoblast within the chorionic villi. They originate from the trophectoderm of the blastocyst during implantation and serve as progenitors for two major trophoblast lineages: the multinucleated syncytiotrophoblast, formed by the fusion of cytotrophoblasts, and extravillous trophoblasts that invade the maternal decidua.

They reside at the base of the chorionic villi, contributing to the formation of the cytotrophoblastic shell that helps anchor the villi to the placental bed. Through fusion, cytotrophoblasts supply the syncytiotrophoblast, the continuous outer layer that directly contacts maternal blood and mediates nutrient exchange, hormone production, and immune interactions.

Cytotrophoblasts can differentiate into extravillous trophoblasts (EVTs), which migrate into the decidua and remodel maternal spiral arteries to establish adequate placental blood flow. EVTs also participate in shaping maternal immune tolerance at the interface of the placenta and uterus.

In health, cytotrophoblasts maintain a balance between proliferation and differentiation. Dysregulation can be associated with placental pathologies, including disorders of placental perfusion such as preeclampsia or fetal growth restriction, and abnormal trophoblast proliferation is observed in gestational trophoblastic diseases.