In the human, trophoblastic cells over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa on about the 6th dayImplantation: The second week of human development is concerned with the process of implantation and the differentiation of the blastocyst into early embryonic and placental forming structures.Implantation commences about day 6Adplantation - begins with initial adhesion to the uterine epithelium (blastocyst then slows in motility, "rolls" on surface, aligns with the inner cell mass closest to the epithelium and stops)Implantation - migration of the blastocyst into the uterine epithelium, process complete by about day 9Coagulation plug - left where the blastocyst has entered the uterine wall day 12Normal Implantation Sites - in uterine wall superior, posterior, lateral