In recent years, the data have been obtained for the effectiveness of the combined use of MF and letrozole, an aromatase inhibitor that is widely used to restore the ovarian cycle and induction of ovulation and improves oocyte implantation and pregnancy rates in women with PCOS, primarily those with reduced sensitivity to CC [144,148,150]. This evidence concerns the gene CYP19A1 and polycystic ovary syndrome.