Syncytiotrophoblast (from the Greek 'syn'- "together"; 'cytio'- "of cells"; 'tropho'- "nutrition"; 'blast'- "bud") is the epithelial covering of the highly vascular embryonicplacentalvilli, which invades the wall of the uterus to establish nutrient circulation between the embryo and the mother. It is a unique tissue in that it is a multi-nucleated, terminally differentiated syncytium, extending to 13m². It lacks proliferative capacity and instead is maintained by fusion of underlying cytotrophoblast cells.
It is the outer syncytial layer of the trophoblasts and actively invades the uterine wall, rupturing maternal capillaries and thus establishing an interface between maternal blood and embryonic extracellular fluid, facilitating passive exchange of material between the mother and the embryo.
Musicki B, Pepe G, Albrecht E (1997). "Functional differentiation of placental syncytiotrophoblasts during baboon pregnancy: developmental expression of chorionic somatomammotropin messenger ribonucleic acid and protein levels.". J Clin Endocrinol Metab82 (12): 4105–10. doi:10.1210/jc.82.12.4105. PMID9398722.Article