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.

Too much or too little FSH can cause a variety of problems, including infertility (the inability to get pregnant), menstrual difficulties in women, low sex drive in men, and early or delayed puberty in children.

Other names: follitropin, FSH, follicle-stimulating hormone: serum

What is it used for?

FSH works closely with another hormone called luteinizing hormone to control sexual functions. So a luteinizing hormone test is often done along with an FSH test. These tests are used in different ways, depending on whether you are a woman, man, or child.

In women, these tests are most often used to:

• Help find the cause of infertility
• Find out if there is a problem with ovarian function
• Find the reason for irregular or stopped menstrual periods
• Confirm the start of menopause, or perimenopause. Menopause is the time in a woman’s life when her menstrual periods have stopped and she can’t become pregnant anymore. It usually starts when a woman is around 50 years old. Perimenopause is the transition period before menopause. It can last for several years. FSH testing may be done towards the end of this transition.

In men, these tests are most often used to:

• Help find the cause of infertility
• Find the reason for a low sperm count
• Find out if there is a problem with the testicles

In children, these tests are most often used to help diagnose early or delayed puberty.

• Puberty is considered early if it starts before age 9 in girls and before age 10 in boys.
• Puberty is considered delayed if it hasn’t started by age 13 in girls and by age 14 in boys.