Letrozole is a highly potent, non-steroidal third-generation aromatase inhibitor. It functions by binding competitively and reversibly to the heme group of the aromatase enzyme (Cytochrome P450 19), completely halting the conversion of androgen precursors into estrogens (estrone and estradiol) in peripheral tissues. In fertility protocols, this sharp drop in circulating estrogen levels removes negative feedback on the hypothalamus and pituitary gland. This triggers a compensatory surge in endogenous FSH secretion, stimulating robust ovarian follicle development and inducing ovulation in patients with Polycystic Ovary Syndrome (PCOS).