Serum Oocyte Stimulating Hormone, also known as Follicle Stimulating Hormone, can be used to view ovarian function in women. It is secreted by the pituitary gland and is elevated when estrogen levels are lowered and elevated when estrogen levels are raised. Follicle stimulating hormone encourages follicle development and also secretes estrogen to maintain normal hormone levels, which are regulated by estrogen. It is used clinically as an indicator of ovarian function. In normal women of childbearing age, it is usually between 5 and 10 U/L, and reaching 20 U/L indicates a decline in ovarian function. Estrogen declines rapidly in postmenopausal women, and follicle-stimulating hormone usually exceeds 40 U/L.