Endometrial and follicular development following letrozole intervention in unexplained infertile patients failed to get pregnant with clomiphene citrate

Purpose  This study is designed to evaluate and compare follicular phase parameters during ovarian stimulation with the clomiphene citrate (CC) and letrozole (LET) in unexplained infertile patients who failed to get pregnant following frequent CC-treated cycles. Methods  A total of 64 unexplained infertile women who failed to get pregnant following frequent CC-treated cycles were studied for one CC-treated cycle (100 mg/day), 2 washout cycles, and then 1 LET-treated cycle (5 mg/day). Number of follicles over 14 mm in diameter, diameter of the largest follicles, endometrial thickness, serum estradiol (E2) and LH levels were measured when one mature follicle over 18 mm in diameter detected during transvaginal ultrasonography. Results  The mean value of the largest follicle diameter, number of developed follicles >14 mm, endometrial thickness and LH in LET-treated cycle was significantly higher than CC-treated cycle (P values were 0.007, <0.001, <0.001, and 0.004, respectively), whereas mean level of E2 showed a significantly lower level during LET-treated cycle (P < 0.001). Conclusions  About 5 mg/day of LET is associated with better follicular phase parameters, endometrial development, serum E2 and LH levels in women with unexplained infertility who failed to get pregnant following frequent CC-treated cycles.