This progression of preimplantation events in the embryo is essential for implantation, and occurs within a narrow time frame during the midsecretory phase.As addressed in later sections, the endometrium is now thought to become permissive to implantation during cycle days 20–24 of a normalized 28-day cycle, the so-called window of receptivity.Schematic showing the different stages of implantation (I–V).Stage I begins with fertilization in the Fallopian tube.
Such methods to weaken the ZP allow for zona shedding that has improved implantation rates, in particular for older women or for prior implantation failures.
In this chapter we briefly describe a variety of animal models of implantation, then outline the classic studies that form the foundation of our current understanding of human implantation.
Finally, we detail the known biochemical markers of uterine receptivity and describe their regulation.
Once contact is made, these appendages invade between uterine epithelial cells into the basal lamina and underlying stroma, thus making the guinea pig a useful model for the study of epithelial penetration.
Such models may provide the most intimate look at the earliest moments of embryo-endometrial interaction (Fig. Through the collective use of these various models, much has been learned about the basic principles of implantation.