A randomized comparison of two ovarian stimulation protocols with gonadotropin-releasing hormone (GnRH) antagonist cotreatment for in vitro fertilization commencing recombinant follicle-stimulating hormone on cycle day 2 or 5 with the standard long GnRH agonist protocol.

Extending the FSH window for multifollicular development by administering FSH from the midfollicular phase onward constitutes a novel mild protocol for ovarian stimulation for in vitro fertilization (IVF) based on the physiology of single dominant follicle selection in normo-ovulatory women. We compared outcomes from this protocol with two other stimulation protocols. One hundred and forty-two normo-ovulatory patients with an indication for IVF (or IVF/ICSI) were randomized to a GnRH agonist long protocol (group A; n = 45) or one of two GnRH antagonist protocols commencing recombinant FSH on cycle d 2 (group B; n = 48) or cycle d 5 (group C; n = 49). A fixed dose (150 IU/d) of rFSH was used for ovarian stimulation, and GnRH antagonist cotreatment was initiated on the day when the leading follicle reached 14 mm diameter. Group C showed a shorter duration of stimulation (median duration, 11, 9, and 8 d for groups A, B, and C, respectively; P < 0.001), reflected in a significantly lower total dose of rFSH used (median amount of rFSH, 1650, 1350, and 1200 IU for groups A, B, and C, respectively; P < 0.001). In group C more cycles were cancelled during the stimulation phase due to insufficient response, resulting in a lower percentage of oocyte retrievals (84%, 73%, and 63% for groups A, B, and C; P = 0.02). However, women in group C obtained better quality embryos (percentage of embryo score of 1 for best embryo, 29%, 37%, and 61% for groups A, B, and C, respectively; P = 0.008), resulting in more transfers per oocyte retrieval (68%, 71%, and 90% for groups A, B, and C, respectively; P = 0.04). After profound ovarian stimulation (groups A and B) only 7% of the patients who retrieved four oocytes or less conceived, whereas after mild stimulation (group C) 67% of these patients conceived (P < 0.01). Overall, no differences were found among the three groups comparing pregnancy rate per started IVF cycle. In conclusion, application of the described mild ovarian stimulation protocol resulted in pregnancy rates per started IVF cycle similar to those observed after profound stimulation with GnRH agonist cotreatment despite shorter stimulation and a 27% reduction in exogenous FSH. A higher cancellation rate before oocyte retrieval was compensated by improved embryo quality concomitant with a higher chance of undergoing embryo transfer. A relatively low number of oocytes retrieved after mild ovarian stimulation distinctly differs from the pathological reduction in the number of oocytes retrieved after profound ovarian stimulation (poor response) associated with poor IVF outcome. The relatively small number of oocytes obtained after mild ovarian stimulation may represent the best of the cohort in a given cycle.