Objective: To compare ongoing implantation rates under two different GnRH antagonist protocols.
Design: Randomized controlled trial.
Setting: Tertiary referral center.
Patient(s): One hundred eleven women undergoing ovarian stimulation for in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI).
Intervention(s): 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 > or = 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.
Main outcome measure(s): Ongoing implantation and pregnancy rate.
Result(s): In patients with no follicle of > or = 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 E2 from initiation of stimulation to antagonist administration was able to distinguish between pregnant and nonpregnant patients in the population studied.
Conclusion(s): High exposure of the genital tract to LH and E2 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.