Journal of Research in Medical Sciences1735-199511620061228Comparison of the success rate of letrozole and clomiphene citrate in women undergoing intrauterine insemination382387ENRobabDavarResearch and Clinical Center for Infertility, Shahid Sadoughi University. r_davar@yahoo.comMaryamAsgharniaMojganJTayebi2006021020060731BACKGROUND: This study was conducted to compare the success rate of daily administration of aromatase inhibitor letrozole at a dose of 5 mg when administrating clomiphene citrate (CC) 100 mg daily in women undergoing superovulation and IUI. METHODS: This prospective randomized trial was done in Research and Clinical Center for Infertility (Shahid Sadoughi University), Yazd, Iran. Ninety-five patients with unexplained and mild male factor infertility were studied. Using a computer-generated random table, the patients were randomized into two groups, which were treated with 5 mg of letrozole daily (42 patients, 42 cycles) or 100 mg of CC daily (53 patients, 53 cycles). The data were analyzed using Student's t-test and chi square test. RESULTS: The mean age and duration of infertility in both groups were similar. There was a significant difference between the two groups in the total numbers of follicles during stimulation (5.45 ± 4.2 in CC group vs. 3.07 ± 2.1 in letrozole group) (P = 0.01). No significant difference in the endometrial thickness was found between the two groups (letrozole group = 6.9 ± 2.2, CC group = 7.8 ± 1.8). The mean levels of LH and FSH in both groups were similar. P value of difference in hormone levels between two groups were 0.33 and 0.47, respectively, but there was a significant difference in mean E2 levels between the two groups (241.28 ± 167.537 in letrozole group vs. 867.34 ± 296.689 in CC group) (P = 0.018). The mean number of gonadotropin ampules used in both groups was the same. Pregnancy rate per cycle was 9.5% in the letrozole group and 5.7% in the CC group (P = 0.6). Two out of the three pregnancies in the CC group (66.6%) and one out of the four pregnancies in the letrozole group resulted in a miscarriage (25%). One twin pregnancy (33%) occurred in the letrozole group and none in the CC group. Ovarian hyperstimulation syndrome (OHSS) did not occur in either of the two groups. CONCLUSIONS: In IUI, superovulation with clomiphene citrate and letrozole was associated with similar pregnancy rates, but the miscarriage rate was higher with clomiphene citrate. KEY WORDS: IUI, letrozole, clomiphene citrate, superovulation.