ABSTRACT
Embryonic implantation, the process by which the human embryo orientates towards, attaches to, and finally invades the underlying maternal endometrial tissue, requires a receptive endometrium, a functionally normal blastocyst, and adequate crosscommunication between them. During apposition, human blastocysts find a location in which to implant, being guided to a specific area in the maternal endometrium. In the adhesion phase, which occurs 6-7 days after ovulation, within the so-called “implantation window,” direct contact occurs between the endometrial epithelium (EE) and the trophectoderm (TE). Finally, in the invasion phase, the embryonic trophoblast traverses the basement membrane and passes the endometrial stroma and reaches the uterine vessels.
