Initiation of gonadotropin-releasing hormone antagonist on day 1 as compared to day 6 of stimulation: effect on hormonal levels and follicular development in in vitro fertilization cycles.

The objective of the present study was to assess the effect of altering the timing of GnRH antagonist initiation on the hormonal environment and follicular development in in vitro fertilization cycles. Sixty women undergoing in vitro fertilization participated in a prospective randomized controlled trial. Patients were stimulated with a fixed dose of 200 IU recombinant FSH, starting on d 2 of the cycle, and with GnRH-antagonist, starting either on d 1 (n = 30) or on d 6 of stimulation (n = 30). A significantly lower exposure to LH (P < 0.001) and estradiol (P < 0.001) during the follicular phase was observed in the d-1 group, compared with the d-6 group of antagonist administration. No differences in follicular development were seen between the two groups on either d 6 of stimulation or on the day of human chorionic gonadotropin administration. Similar fertilization rates, implantation rates, and ongoing pregnancy rates per transfer were, in addition, present between the two groups compared. In conclusion, administration of GnRH antagonist on d 1 (compared with d 6) of stimulation is associated with a lower exposure to LH and estradiol, which does not seem to affect follicular development.