syn = together + kytos = hollow vessel + trophe = nourishment + blastos = germ; outer layer of epithelium covering chorionic villi of conceptus.

The component of the trophoblast bathed by maternal blood in the placenta (and thus covering the chorionic villi). Derived by differentiation and fusion of cytotrophoblast cells, so the syncytiotrophoblast only ever comprises just one cell (albeit with very many cell nuclei), through which almost everything reaching or leaving the embryo or fetus must pass. By the end of normal pregnancy, its area is about 12 square meters, or over 100 square feet. Most hormones and proteins produced by the placenta, such as progesterone, hCG and PAPP-A, come from it. See also: lacunae

This is a specialized cell of the placenta (also a trophoblast) which acts like a dialysis membrane between the mothers blood and the babies blood, feeding the baby as well as removing waste products from the babies blood.