Use of GNRH antagonists in reproductive medicine.

Gonadotrophin-releasing hormone (GnRH) plays a key role in the secretion of gonadotrophins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which regulate steroidogenesis and folliculogenesis. Two GnRH antagonists, Cetrorelix and Ganirelix, deprived of histaminergic side-effects, have been introduced into ovarian stimulation protocols to prevent premature LH surges and proved their safety in clinical trials. At present, most of the published studies have not found significant differences in follicular recruitment, oocyte quality, and so on, except for a decrease in pregnancy and implantation rates in in vitro fertilization and embryo transfer (IVF-ET) cycles when the GnRH antagonist rather than the agonist was used. This decrease in pregnancy rates was in relation with a necessary learning curve of the physicians. Another possibility is the impact of the GnRH antagonist on endometrium through its GnRH receptor; this effect was cancelled after cryopreserved embryo transfers because the pregnancy rates were similar between GnRH antagonist and agonist in this case. GnRH antagonists were also interesting in poor responders and polycystic ovarian syndrome, where the agonists have not permitted to obtain the better results in IVF-ET cycles. Similarly, the GnRH antagonists could prevent the LH surge in the intrauterine insemination cycles.