syncytiotrofoblasto

The syncytiotrophoblast is a multinucleated cell layer forming the outermost layer of the placental villi, derived by fusion of cytotrophoblast cells and lining the continuous surface of the chorionic villi in direct contact with maternal blood in the intervillous space. It is essential for implantation and placental function throughout pregnancy.

During placental development, cytotrophoblasts proliferate and fuse to form a syncytial layer. This syncytium lacks distinct cell boundaries and forms microvilli on the surface to maximize exchange area. It remains in contact with maternal blood and is renewed over time by incorporation of new cytotrophoblast.

Functions include endocrine and transport roles. Endocrine: it produces hormones including human chorionic gonadotropin (hCG), placental lactogen, progesterone, and estrogens. It participates in nutrient and gas exchange between mother and fetus and serves as a selective barrier at the maternal-fetal interface. It also contributes to immune regulation at the implantation site, helping to maintain tolerance to the fetus.

Clinical significance: the activity of the syncytiotrophoblast underpins pregnancy testing via hCG production. Abnormalities in its development or function are associated with placental pathologies such as preeclampsia, intrauterine growth restriction, and molar pregnancies, and it is a key site of trophoblastic diseases.