ABSTRACT
Implantation is a complex phenomenon, still not thoroughly understood, involving the embryo and the endometrium.1 Implantation has been considered as a gradual process requiring embryo adhesion to the luminal surface of the endometrium, followed by invasion of the trophectoderm cells from the embryo, through the luminal epithelium, into the deeper layer of the endometrium.2,3 These complex molecular interactions between the uterus and the mature blastocyst are necessary to establish the uteroplacental circulation and finally lead to implantation, approximately six or seven days after fertilization.1,4 By the 10th day after fertilization, the blastocyst is completely embedded in the stromal tissue of the uterus, leading to cytotrophoblast invasion into the entire endometrium and the inner third of the myometrium, as well as the uterine vasculature.5
