In the pre-menopausal woman treated for infertility with letrozole, estradiol can still be produced during the follicular phase of the menstrual cycle, either because of a reduction in letrozole availability due to letrozole’s half-life, the treatment regimen, or because of enhanced aromatase expression primarily due to increased FSH and FSH receptor availability. This evidence concerns the gene BRD2 and Infertility.