The placenta develops from trophectoderm of the blastocyst through the processes of cell proliferation and differentiation. It consists of an outer layer of trophoblasts and an inner connective tissue core with macrophages (Hofbauer cells), fibroblasts, and blood vessels branched out from the umbilical vessels. The trophoblast layer and connective tissue core communicate with each other through the molecules made by each of them. The trophoblast cell layer contains outer syncytiotrophoblasts and inner mononuclear cytotrophoblasts and extravillous mononuclear trophoblasts that invade the uterus to establish a vascular connection with the maternal circulation.1 Signals of invasion may come from syncytiotrophoblasts through human chorionic gonadotropin (hCG).2,3,4 and 5 Villus and extravillus cytotrophoblasts can proliferate and are relatively inactive in the synthesis of many placental hormones. Upon appropriate stimulation, villus cytotrophoblasts can undergo aggregation and fusion of their plasma membranes to become syncytiotrophoblasts, which are terminally differentiated and serve as the primary source of many placental hormones and other regulatory agents. The placenta deters the noxious agents and yet allows nutrients to enter the fetal circulation and fetal metabolic waste to empty into the maternal circulation, while preventing maternal immune system cells from attacking the fetus. Structural features, and the ability to produce a wide array of regulatory molecules, allow the placenta to grow, to differentiate, and to perform numerous diverse functions, including possible communications with the brain.6,7,8 and 9