When given to a woman for fertility reasons (usually someone who’s ovaries are not producing an egg), the Letrozole blocks the production of estrogen elsewhere in the body. When estrogen is blocked, the pituitary gland gets a message that it needs to produce follicle-stimulating hormone (FSH), which stimulates the ovary to produce an egg. Some women on letrozole actually release more than one egg because they produce more FSH while on letrozole than a woman produces when ovulating naturally.
Hope this is helpful @kmakm