Clomiphene citrate versus letrozole for ovarian stimulation: a pilot study

The purpose of this pilot study was to compare the endocrinological environment of cycles stimulated with clomiphene citrate (CC) or letrozole. Fifteen patients undergoing intrauterine insemination (IUI) received from day 3 to day 7 of the cycle either letrozole 2.5 mg/day (n = 7) or clomiphene citrate 100 mg/day (n = 8). IUI was performed one day after the detection of LH peak. No luteal support was administered. Significantly lower serum oestradiol concentrations were present in the follicular phase on days 9, 13 and 15 of the cycle and in the luteal phase on days 3 and 6 post-IUI in the letrozole group compared with those in the CC group. Progesterone concentrations and oestradiol concentrations were significantly lower in the letrozole group than in the CC group on the day of LH peak. Significantly more follicles developed in patients in the CC group compared with those in the letrozole group. In conclusion, significantly lower oestradiol concentrations and fewer follicles are observed in cycles stimulated with 2.5 mg letrozole compared with cycles stimulated with 100 mg CC from day 3 to day 7 of the cycle.