A comparison of the use of clomiphene citrate and letrozole in patients undergoing IVF with the objective of producing only one or two embryos

The objective of this study was to compare the use of clomiphene citrate and letrozole in an IVF setting in which the objective was to produce only one or two embryos. Either clomiphene citrate or letrozole was used in conjunction with gonadotropins without the use of GnRH antagonists. Sixty-two patients received either clomiphene citrate or letrozole with low dose gonadotropins in 128 non-randomized treatment cycles. HCG was given when one follicle was at least 17 mm. Oocyte retrieval was done 34 hours later and fertilization was performed using ICSI. There were no statistically significant differences in the number of large follicles produced, oocytes fertilized, endometrial thickness, clinical pregnancy rates, or delivery rates in patients taking letrozole compared to clomiphene citrate. More mature oocytes were retrieved after clomiphene citrate, but a subset analysis of patients undergoing both treatments did not support this difference. The only statistically different finding in both analyses was the peak estradiol levels during treatment, which averaged 516 pg/ml with letrozole and 797 pg/ml with clomiphene citrate (p = 0.005). Overall, the cancellation rate due to a premature LH surge was 5%. An average of 2.8 mature oocytes were recovered, 2.1 oocytes fertilized and 1.6 embryos were transferred. The overall clinical pregnancy rate per transfer was 25% (95% confidence interval 17.7% to 33.3%) and the overall live birth rate per transfer was 19.2% (95% confidence interval of 11.6% to 26.8%). Other than peak estradiol levels, there were no clinically significant differences when letrozole or clomiphene citrate was used for mild ovarian stimulation for IVF. There were only rare cancellations because of premature LH surges.