Prolongation of the follicular phase in in vitro fertilization results in a lower ongoing pregnancy rate in cycles stimulated with recombinant follicle-stimulating hormone and gonadotropin-releasing hormone antagonists.

To assess the effect of altering the timing of hCG administration on ongoing pregnancy rates in patients stimulated with recombinant FSH (rec-FSH) and GnRH antagonists for IVF. Prospective, randomized, controlled trial. Tertiary referral center. Four hundred thirteen patients undergoing IVF. Rec-FSH stimulation starting on day 2 of the cycle combined with daily GnRH antagonist starting on day 6 of stimulation. Patients were randomized to receive 10000 IU of hCG either as soon as at least three follicles were >or=17 mm on ultrasound (early-hCG group, 208 patients) or 2 days later after this criterion was met (late-hCG group, 205 patients). Ongoing pregnancy rate. Fertilization rates and number and quality of embryos transferred did not differ between the two groups. However, a significantly lower ongoing pregnancy rate was present in the late-hCG as compared with the early-hCG group (25.0% vs. 35.6%, respectively). Prolongation of the follicular phase in patients stimulated with rec-FSH and GnRH antagonists for IVF does not affect oocyte or embryo quality but is associated with a significantly lower ongoing pregnancy rate.