Folliculogenesis in women is a dynamic and uninterrupted process from fetal life until menopause. During follicle growth, the oocyte undergoes functional changes in order to become fertilizable at ovulation. However, various factors derived from the oocyte seem to play a crucial role for preantral follicle development. The growth of large antral follicles is depended on gonadotrophins. These hormones are obligatory for follicle maturation during the follicular phase of the cycle. Although follicle stimulating hormone (FSH) is important for follicle growth, steroidogenesis in the early follicular phase is the result of the cooperation of FSH and luteinizing hormone (LH) in the context of the two-cell two-gonadotrophin theory. The dual action of LH might have a potential application in IVF programs to control the number of follicles that develop during the exogenous administration of FSH, particularly in patients prone to excessive response of the ovaries, such as in polycystic ovary syndrome.