[Comparison of GnRH agonists and antagonists in an ovular donation program]

GnRH agonists and antagonists are utilized for avoiding premature ovulation in assisted reproductive cycles, (ART) this retrospective study was designed to compare both treatments in controlled ovarian hyperstimulation (HOC) in oocyte donors.

Between Jan99 and Mar03, 141 oocyte donors underwent ART receiving either 0.25 mg daily of a GnRH antagonist (Cetrorelix) from day 6 of stimulation (51 patients) or a long protocol with a GnRH agonist (Leuprolide acetate) (90 patients.) FSHr alone or with HMG or LHr were employed for ovarian stimulation. hCG (Profasi, Serono) was administrated when more than three follicles above 18 mm in diameter were observed, oocyte retrieval was performed 34 hours later. Embryo transfer was performed 3-5 days later.

Both groups were homogeneus for age (p=0.142), day 3 FSH (p=0.115), type and total dose of gonadotrophins utilized. There were no significant differences in follicles number (p=0.522), oestradiol levels on the day of hCG (p=0.310) and fertilization rates (p=0.177) The mean number of oocytes retrieved and metaphase II oocytes was significantly lower in GnRH agonist group, (12 vs. 13.9, p=0.05 and 8.6 vs 11; p=0.007) There was no statistical differences in pregnancy and implantation rates between agonist and antagonist groups (52.2% vs 60.8%, 15.1% vs 18.3%; p=0.327 and 0.652).

The high number of metaphase oocytes and the high pregnancy rate observed in the oocyte donors provide evidence that GnRH antagonist does not impair ovarian response, embryo quality or pregnany rates. In oocyte donors cycles the GnRH antagonist is a valid alternative to GnRH agonist, providing the benefit of more flexibility in patient's scheduling.