Embryo implantation and GnRH antagonists: ovarian actions of GnRH antagonists

The gonadotrophin-releasing hormone (GnRH) antagonists, cetrorelix and ganirelix, have both been approved for ovarian stimulation to prevent a premature LH surge. Since GnRH receptors and their gene expression have been detected in human ovary, concern has risen over whether GnRH antagonists might affect ovarian function. Three large trials which compared GnRH agonists (used in the standard protocol worldwide), with the new antagonist treatment found no significant differences concerning the most important goals, e.g. pregnancy rate, fertilization and quality of oocytes. However, the concentration of oestradiol, and the pregnancy and implantation rates were lower in GnRH antagonist-treated patients. These findings again fuelled the debate about the possible extrapituitary effects of GnRH antagonists. Here, we review the conflicting data in the literature on the ovarian effects of GnRH antagonists and discuss our own results. In our view, it is unlikely that GnRH antagonists have a relevant impact on ovarian steroidogenesis and function; however, GnRH antagonists may exert other effects on the ovary.