Anastrozole or letrozole for ovulation induction in clomiphene-resistant women with polycystic ovarian syndrome: a prospective randomized trial

Objective: To compare the effects of letrozole (2.5 mg) and anastrozole (1 mg) meant for ovulation induction in clomiphene (CC)-resistant women with PCOS. Design: Prospective randomized trial. Setting: University teaching hospital and private practice setting. Patient(s): The study comprised a total of 220 infertile women (574 cycles) with CC-resistant PCOS. Intervention(s): Patients were randomized to treatment with 2.5 mg of letrozole daily (111 patients, 295 cycles) or 1 mg of anastrozole daily (109 patients, 279 cycles) for 5 days from day 3 of menses. Main Outcome Measure(s): Number of follicles, serum E-2, serum P, endometrial thickness, pregnancy rate (PR), and miscarriage rate. Result(s): The total number of follicles was significantly more in the anastrozole group (5.4 +/- 0.4 vs. 5.8 +/- 0.4). The number of follicles >= 14 mm (3.1 +/- 0.3 vs. 2.7 +/- 0.2) and >= 18 mm (2.3 +/- 0.1 vs. 3.1 +/- 0.2) were significantly higher in the anastrozole group. The endometrial thickness at the time of hCG administration was significantly more in the anastrozole group (9.1 +/- 0.2 vs. 10.2 +/- 0.7 mm). The duration to reach a dominant follicle was longer in the letrozole group (12.1 +/- 1.3 days vs. 8.8 +/- 1.9 days) but without statistical significant difference. Ovulation occurred in 183/295 cycles (62%) in the letrozole group and 177/279 cycles (63.4%) in the anastrozole group, whereas pregnancy occurred in 36/295 cycles (12.2%) in the letrozole group and 42/279 cycles (15.1%) in the anastrozole group and the differences were not statistically significant. Conclusion(s): The results of this study did not show a significant difference in PR or miscarriage rate between anastrozole and letrozole when used for ovulation induction in women with CC-resistant PCOS.