FSH (follicle-stimulating hormone) is a hormone synthesized by the pituitary gland, a small gland at the base of the brain. FSH is associated with the menstrual cycle and the development of eggs in women and with sperm production in men. In women, the FSH test is indicated in cases of infertility, menstrual cycle disorders and menopause.
In men, the test is indicated in cases of infertility. Unlike in men, FSH secretion in women varies depending on the stage of the menstrual cycle: at the beginning of the cycle, it increases, with stimulation of estradiol production and maturation of an ovum. At mid-cycle, there is a spike in FSH secretion and LH that causes ovulation. In the last two weeks of the cycle, levels of FSH gradually decrease until menstruation begins. Levels of FSH should therefore be interpreted in light of other laboratory results (LH, estradiol, progesterone, inhibin, testosterone). In menopausal women, there is an increase in FSH secretion by the pituitary gland in an attempt to restimulate estradiol production by the ovaries, which are no longer functional.
High levels of FSH in an infertile individual indicate that it is the sex organs (ovaries, testicles) that are impaired rather than the pituitary. Low levels of FSH will instead direct the investigation to a pituitary condition. A high result in perimenopausal women with low estradiol levels helps confirm the onset of menopause.