Comparison of the efficacy of the aromatase inhibitor letrozole and clomiphene citrate as adjuvants to recombinant follicle-stimulating hormone in controlled ovarian hyperstimulation: a prospective, randomized, blinded clinical trial

ObjectiveTo study the efficacy of the aromatase inhibitor letrozole as adjuvant to recombinant FSH (rFSH) in controlled ovarian hyperstimulation (COH).DesignProspective, randomized, and blinded clinical study.SettingAcademic tertiary institute.Patient(s)Forty-one patients with unexplained infertility undergoing intrauterine insemination (IUI) therapy were randomized to receive either letrozole or clomiphene citrate (CC) as adjuvants to rFSH.Intervention(s)From day 3 to 7 of the cycle 2.5 mg/d letrozole or 100 mg/d CC were administrated. All patients received 75 IU rFSH starting on day 7 of stimulation until the day of hCG administration. Ovulation was triggered with recombinant hCG (250 μg) when the leading follicle(s) reached 18 mm in diameter. A single IUI was performed 36 hours later. The luteal phase was supplemented with micronized progesterone vaginally.Main Outcome Measure(s)Ovarian stimulation response (E2 levels and number of follicles) was our primary outcome.Result(s)There were no differences in demographic characteristics between groups. Although there was a significantly lower peak serum E2 level in the group receiving letrozole + rFSH compared with CC + rFSH (914 ± 187 vs. 1,207 ± 309 pg/mL, respectively; P<.007), there were no differences in the number of mature (>16 mm) preovulatory follicles. A significantly higher endometrial thickness was observed at the time of hCG administration in patients that received letrozole (9.5 ± 1.5 mm vs. 7.3 ± 1.1 mm; P=.0001). The clinical pregnancy rate was similar between groups (23.8% vs. 20%, respectively).Conclusion(s)The aromatase inhibitor letrozole appears to constitute a good alternative to CC in patients with unexplained infertility undergoing gonadotropin-stimulated COH cycles combined with IUI therapy.