The inner cell mass gives increase to the fetus, while the surrounding trophectoderm transforms into the placenta.DAYS 6-7Six to 7 dpf, the blastocyst connects to the uterine wall and starts its invasion.1 DAYS 7-9After implantation, the trophectoderm starts improving the endometrium. From weeks 3 to 10, cytotrophoblast cells get away into the decidua, a specialized layer of endometrium, and distinguish into extravillous trophoblasts. These attacking cells remodel spiral arteries to reroute adult blood to the intervillous area.2 By the beginning of the 2nd trimester, the cytotrophoblast plug breaks down and parental blood begins to get in the intervillous space.ReferencesTurco MY, Moffett A. Development of the human placenta.