A randomized trial of letrozole versus clomiphene citrate in women undergoing superovulation.

Objective: To compare the effects of the aromatase inhibitor letrozole (7.5 mg) and clomiphene citrate (CC; 100 mg) in women undergoing superovulation and IUI.

Design: Prospective randomized trial.

Setting: University teaching hospital.

Patient(s): We studied a total of 238 cycles of superovulation and IUI in women with idiopathic infertility.

Interventions: Patients were randomized into treatment with 7.5 mg of letrozole daily (74 patients, 115 cycles) or 100 mg of CC daily (80 patients, 123 cycles).

Main Outcome Measure(s): Number of follicles, endometrial thickness, pregnancy rate, and miscarriage rate.

Result(s): The mean age, parity, and duration of infertility in both groups of patients were similar. There was no significant difference between the total number of developing follicles in the letrozole (5.7 +/- 3.7) and in the CC groups (4.8 +/- 2.5). The number of follicles of > or =14 mm and of >18 mm were 2.1 +/- 1.2 and 1.4 +/- 0.7 in the letrozole group, and 1.7 +/- 0.9 and 1.1 +/- 0.5 in the CC group, respectively. No difference was found in the endometrial thickness between the two groups (7.1 +/- 0.2 mm in the letrozole group, 8.2 +/- 5.9 mm in the CC group). The pregnancy rate per cycle was 11.5% in the letrozole group and 8.9% in the CC group. Four of the 11 pregnancies in the CC group resulted in a miscarriage (36.6%).

Conclusion(s): Superovulation and IUI with letrozole and CC are associated with similar pregnancy rates, but the miscarriage rate is higher with CC. The ideal dose of letrozole remains unknown and further study is needed.