In almost all studies to date , letrozole was administered for five consecutive days in early follicular phase . In only one study , letrozole (2.5 mg/day) was administered for ten consecutive days starting on day 1 of menstrual cycle . In that study , prolonged administration of letrozole produced more mature follicles and pregnancies than short letrozole therapy regimen in patients with clomiphene citrate resistant polycystic ovary syndrome .