Exposure to high levels of luteinizing hormone and estradiol in the early follicular phase of gonadotropin-releasing hormone antagonist cycles is associated with a reduced chance of pregnancy

To compare ongoing implantation rates under two different GnRH antagonist protocols. Randomized controlled trial. Tertiary referral center. One hundred eleven women undergoing ovarian stimulation for in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI). Ovarian stimulation with 150 IU recombinant-FSH (rec-FSH) starting on day 2 of the cycle and GnRH antagonist starting either on day 6 of stimulation (fixed group) or when a follicle of ≥15 mm was present after at least 5 days of stimulation (flexible group). In the flexible group, the rec-FSH dose was increased to 250 IU when the antagonist was initiated. Ongoing implantation and pregnancy rate. In patients with no follicle of ≥15 mm present on day 6 of stimulation, a significantly lower ongoing implantation rate was observed if the flexible scheme was applied as compared with the fixed scheme of administration (8.8% vs. 23.9%, respectively). Exposure of the genital tract to LH or E 2 from initiation of stimulation to antagonist administration was able to distinguish between pregnant and nonpregnant patients in the population studied. High exposure of the genital tract to LH and E 2 in the early follicular phase is associated with a reduced chance of pregnancy in cycles stimulated with recombinant FSH and GnRH antagonist for IVF/ICSI.