Comparison of Implantation in Utero and in Vitro

Abstract

Because implantation is the increasingly intimate interaction of a blastocyst with the endometrium of an intact uterus, there is really no such thing as in vitro implantation. However, trophoblast in vitro continues to differentiate beyond the preimplantation stage, and double organ culture can be used for cell associations. Therefore, it is possible to make models, if not of normal implantation, at least of ectopic implantation. The precise morphological events of implantation are sufficiently different in different groups of manmials to preclude all but the broadest generalizations concerning implantation (Wimsatt, 1975; Schlafke and Enders, 1975). In considering those species that have been studied by in vitro implantation models, attention has been confined to examples in which there is considerable invasion of the endometrium. Many domestic animals and most of the marsupials, in which implantation is more superficial, have been excluded from these studies.