Reproductive biology and IVF: ovarian stimulation and endometrial receptivity.

The influence of ovarian stimulation on endometrium receptivity has been inadequately addressed in medical literature. Hormonal effects of ovarian stimulation on endometrial changes as compared with the natural cycle should be elucidated and correlated with the potential of the embryo to implant. It is important to distinguish between the endometrial effect of induction of ovulation in anovulatory women and those of ovarian (super)ovulation in ovulatory women. Induction of ovulation leads to in vivo conception whereas ovarian stimulation results in in vitro fertilization. The available data in the field indicate that endometrial changes have an impressive negative influence on the potential of embryonic implantation. The aim of this review is to analyse the effects of gonadotropin, GnRH-agonist and GnRH-antagonist administration on endometrial behaviour, to highlight the gaps in current knowledge and to propose areas in which research is needed.