Follicle-Stimulating Hormone (FSH) Levels Test

This test measures the level of follicle-stimulating hormone (FSH) in a sample of your blood. A hormone is a chemical messenger in your bloodstream that controls the actions of certain cells or organs. FSH plays an important role in sexual development in children and fertility in adults.

In women who menstruate (have periods), FSH helps control the menstrual cycle. It triggers the growth of eggs in the ovaries and gets the eggs ready for ovulation. Ovulation is when an ovary releases an egg so it can travel down a fallopian tube where it can be fertilized by sperm.; In men, FSH helps control the amount of sperm that the testicles (testes) make.

It also affects how healthy the sperm are.; In children, FSH levels are normally low until puberty starts. Then FSH levels begin to rise along with the levels of other hormones. The increase in all these hormones triggers the physical changes of puberty: In girls, FSH tells the ovaries to start making the hormone estrogen.

Estrogen is involved in the growth of breasts, body hair, and menstruation.; In boys, FSH tells the testicles to start making the hormone testosterone. Testosterone is involved in the growth of facial and body hair, changes in a boy's voice, and sperm production.; ; FSH levels are controlled by a complex system of hormones made in different parts of your body. Abnormal levels of FSH may be a sign of a problem with any of these parts.

They include your: Pituitary gland, a small gland at the base of your brain. It makes FSH.; Hypothalamus, a part of your brain. It makes hormones that tell your pituitary gland how much FSH to make.; Reproductive glands, your ovaries or testicles.

The amount of sex hormones they make let your hypothalamus and pituitary gland know when to start and stop making FSH.;

Why this test is done

For women:

You may need this test if:

• You've been unable to get pregnant after 12 months of trying.

Your menstrual periods aren't regular or have stopped.

If you're age 45 or older, testing usually isn't needed. That's because high levels of FSH are a normal sign of perimenopause and menopause. As your ovaries release fewer eggs, your body makes more hormones to try to trigger ovulation.

But you may need an FSH test along with other hormone tests if there is a medical reason, including:

• Premature menopause (age 40 or younger)
• Early menopause (before age 45)
• Having symptoms that may be related to menopause, but the cause isn't clear
• You have a less interest in sex than usual.

For men:

You may need this test if:

• You've been unable to get your partner pregnant after 12 months of trying.
• You have less interest in sex than usual.
• You have a low sperm count.
• You have a loss of muscle and/or body hair.

For women and men:

You may need an FSH test if your health care provider thinks you could have a pituitary disorder. Pituitary problems can affect fertility and decrease your interest in sex. They may also cause symptoms, such as:

• Fatigue
• Weakness
• Decreased appetite and/or weight loss

Children and teens may need FSH testing if puberty seems to be starting too early or too late:

• Early puberty means showing signs of sexual development before age 8 in girls and age 9 in boys.
• Delayed puberty means not showing signs of sexual development by age 13 in girls and age 14 in boys.

How to prepare

Women who have menstrual periods may need to be tested at a specific time during their menstrual cycle. That's because FSH levels change throughout the month.

Sample type

Blood

Other names for this test

follitropin, FSH, follicle-stimulating hormone: serum, pituitary gonadotropins