This test measures the level of follicle-stimulating hormone (FSH) in your blood. FSH is made by your pituitary gland, a small gland located underneath the brain. FSH plays an important role in sexual development and functioning. In women, FSH helps control the menstrual cycle and stimulates the growth of eggs in the ovaries. FSH levels in women change throughout the menstrual cycle, with the highest levels happening just before an egg is released by the ovary. This is known as ovulation. In men, FSH helps control the production of sperm. Normally, FSH levels in men do not change very much. In children, FSH levels are usually low until puberty, when levels begin to rise. In girls, it helps signal the ovaries to make estrogen. In boys, it helps signal the testes to make testosterone.