Syncytiotrophoblast

Syncytiotrophoblasts are multinucleated cells found in the placenta of embryos.

They are the outer syncytial layer of the trophoblasts and actively invade the uterine wall.

They form the outermost fetal component of the placenta (also known as 'syntrophoblast') and massively increase the surface area available for nutrient exchange between the mother and the fetus.

Cells from the syncytiotrophoblast secrete progesterone in addition to human chorionic gonadotropin (hCG) and human placental lactogen (HPL); hCG prevents degeneration of the corpus luteum. Progesterone serves to maintain the integrity of the uterine lining and, until the syncytiotrophoblast is mature enough to secrete enough progesterone to support pregnancy (in the fourth month of embryonic development), it is aided by the corpus luteum graviditatis.