ABSTRACT
Implantation is difficult to study in any species because of its location and the fact that it is easily perturbed. It is even more difficult to study in the human where ethical considerations prevent manipulation and even observation. Thus much of our knowledge about how the embryo is converted from a blastocyst, free in the uterine lumen, to a conceptus, firmly attached to the uterine wall with placenta formation under way, comes from animal models. A few studies have been carried out on human blastocyst attachment in vitro (Lindenberg et al., 1986, 1989) and data on expression of cell adhesion molecules on human embryos is now starting to appear (Campbell et al., 1995a,b) so that we can begin to predict whether molecules implicated in attachment in other species could also be involved in human.
