Embryo implantation after human in vitro fertilization: importance of endometrial receptivity

To study the effects of controlled ovarian hyperstimulation (COH) on endometrial receptivity during human in vitro fertilization (IVF), we compared embryo implantation data obtained from our nonanonymous donor oocyte program with those obtained from standard IVF. To control for embryo quality, IVF patient characteristics were matched to those of the oocyte donors with regard to age and previous gravidity. All cycles were performed in an identical manner, using standardized ovarian stimulation protocols, transvaginal follicle aspiration, fertilization and culture in vitro, and transcervical embryo transfer. A similar number of oocytes per cycle were obtained, fertilization rates were similar, and similar numbers of embryos were transferred in both groups. Transferred embryos had similar numbers of blastomeres and were morphologically judged to be of similar quality in both groups. Implantation rates per individual embryo were significantly higher in donor than in standard IVF (35% versus 10.7%) as were ongoing per embryo implantation rates (23% versus 8%). Clinical and ongoing pregnancy rates per cycle were likewise higher in the donor group than in the standard IVF group (67% versus 39%, and 61% versus 30%, respectively). We conclude that COH inhibits embryo implantation after IVF by decreasing endometrial receptivity, which is an important factor in IVF pregnancy success.