In the present study, we found that in the first letrozole-IUI cycle, the optimal follicle size before hCG trigger was significantly associated with PR, CPR and LBR, even after adjusting for known confounders including female age, BMI, infertility type, the duration of infertility, infertility diagnosis, endometrium thickness, FSH, AMH, TMC, LH surge and E2 on the day of hCG trigger. This evidence concerns the gene AMH and Infertility.