Letrozole versus Clomiphene Citrate for Induction of Ovulation in Patients with Polycystic Ovarian Syndrome Undergoing Intrauterine Insemination

BACKGROUND Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies affecting women in the reproductive age group, and is one of the most common causes of hyperandrogenic anovulatory infertility. The aromatase inhibitor, letrozole, has been used for induction of ovulation. The purpose of this study was to compare the effects of letrozole and clomiphene citrate in induction of ovulation among patients with PCOS undergoing intrauterine insemination. METHODS In a double-blind randomized study, 60 infertile patients with PCOS received standard doses of either clomiphene citrate or letrozole as an induction protocol prior to intrauterine insemination. A hormonal profile, pelvic ultrasound, hysterosalpingogram, and/ or laparoscopy were done for all patients. The patients were monitored for ovulation by translational ultrasonographic folliculometry, with measurement of number and size of the follicles, as well as endometrial thickness. Human chorionic gonadotrophin (HCG) was injected intramuscularly when at least one mature follicle ≥18 mm diameter was detected, and intrauterine insemination was performed 32-36 hours later. Transvaginal ultrasound and β-HCG measurement were performed for confirmation of pregnancy. RESULTS Letrozole and clomiphene citrate achieved follicle maturation within a mean ± standard deviation (SD) of 13.2 ± 1.53 and 14.1 ± 1.35 days, respectively, showing no significant difference (P > 0.05). The mean number of follicles reaching ≥18 mm on the day of HCG administration was significantly higher in patients who received clomiphene citrate (2.9 ± 1.77) than in those receiving letrozole (1.2 ± 0.9). Letrozole had a significantly greater effect than clomiphene citrate on endometrial thickness (9.16 ± 1.36 versus 4.46 ± 1.71). The number of pregnancies achieved in the letrozole group was significantly (P < 0.05) greater than in the clomiphene group. CONCLUSION Letrozole in patients with PCOS is as effective as clomiphene citrate in inducing ovulation, and although the number of follicles produced by induction with letrozole were less than those produced by clomiphene, letrozole had a significantly greater effect on endometrial thickness than clomiphene citrate, and the incidence of pregnancy after intrauterine insemination was significantly higher, with a lower incidence of multiple pregnancy.