Implantation begins first with attachment (adplantation) of the blastocyst through the outer trophopoblast cells to the uterine lining. Following adplantation, trophoblast cells on the outside differentiate into syncitiotrophoblasts which invade the uterine endometrium. The blastocyst then moves moves into the endometrium, initially partially buried, and on completion of implantation, is fully buried in the endometrium. The site of implantation is marked on the surface by a "plug".
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