A comparison of endometrial thickness following augmentation of ovulation with clomifene citrate or letrozole in women with ovulatory infertility

OBJECTIVES: To compare endometrial thickness following augmentation of ovulation with clomifene (CC) and letrozole and to assess the rate of multi-follicle development and the FSH fluctuations during the stimulated cycles.

METHODS: A comparative study was carried out at the infertility clinic of Faculty of Medicine, University of Kelaniya, Sri Lanka. Each arm included 25 participants. They received either 100 mg of CC or 2.5 mg of letrozole per day for 5 days starting from 2nd day of the cycle. The fluctuation of FSH in the follicular phase of the cycle, the endometrial thickness and the number of pre-ovulatory follicles on the day of detecting a mature follicle, were measured.

RESULTS: Treatment with letrozole resulted in a smaller rise in the follicular phase FSH, which was shorter in duration than with CC. Also it resulted in a higher mean endometrial thickness at the time of detecting a mature follicle [9.89 (SD=2.02) mm vs. 8.58 (SD=1.32) mm; p=0.021]. Augmentation of ovulation with CC showed a trend towards multi-follicle development compared to letrozole.

CONCLUSIONS: This study suggests that letrozole is superior to CC in augmentation of ovulation in terms of endometrial growth and mono-follicle development. However more studies are needed to assess how these differences affect the treatment outcome before it is recommended for clinical use.