What Is Follicle Stimulating Hormone?

Follicle stimulating hormone (FSH) is a hormone made by the pituitary gland. It plays a key role in sexual development.

In kids, FSH levels rise just after birth and peak at about 1 to 3 months. Then they drop and stay low until puberty approaches (usually between ages 10 and 14). The brain makes gonadotropin-releasing hormone (GnRH), which starts the changes toward sexual maturity. GnRH signals the pituitary gland to release two puberty hormones into the bloodstream: FSH and luteinizing hormone (LH).

FSH and LH tell the testes and ovaries to make hormones that bring about changes during puberty, like the development of sperm or eggs.

Why Are FSH Tests Done?

An FSH test measures the level of FSH in the blood. Doctors may order the test if puberty starts earlier or later than expected.

The test also can check for damage or disease of the testes or ovaries, pituitary gland, or hypothalamus (hi-po-THAL-uh-mus), an area of the brain that links the nervous system with the hormone-making endocrine system.

In teens and adults, FSH levels can also help doctors check menstrual problems and fertility issues (trouble having a baby).

Top Things to Know

• The follicle stimulating hormone (FSH) blood test checks how much FSH is in the blood.
• This test may be done to see why puberty is early or late, or for other reasons.
• Kids might need to stop taking certain medicines or not eat or drink before the blood test.
• Your doctor can explain what it means if the FSH level is high or low.

How Can I Help My Child Prepare for a Blood Test?

If your child has already started getting periods, the FSH test might have to be done on a certain day of the menstrual cycle.

To help kids get ready for a blood test, find out if they need to fast (not eat or drink) or should stop taking medicines before the test. Explain what to expect during the test. If your child is nervous about it, work together on ways to stay calm. Deep breathing or even imagining being in a peaceful place that makes your child feel safe and relaxed can help.

What Do FSH Test Results Mean?

Your doctor will explain what the results of the FSH test mean for your child. “Normal” levels vary based on things like age and sex.

FSH levels may be high if puberty is going to start soon.

High FSH Levels

In females, high FSH levels sometimes happen due to pituitary gland problems, hormone therapy, genetic differences like Turner syndrome, or menopause (when periods stop completely).

In males, high FSH levels could mean the testes aren’t working well because of things like radiation therapy, chemotherapy, hormone treatment, a problem with the pituitary gland, or a genetic difference (like Klinefelter syndrome).

Low FSH Levels

Females and males may have low FSH levels if they have a problem with the pituitary gland or hypothalamus, or recently lost weight quickly or are at a very low weight.

Females might also have low FSH levels if they aren’t ovulating (ovaries aren’t releasing eggs) or are pregnant.

What Else Should I Know?

Sex hormones work closely with each other. So doctors might do an FSH test along with other blood tests that measure hormones like:

• LH
• estradiol
• testosterone

Together, the results can give a more complete picture of sexual development.

If you have questions about the FSH test or what the results mean, talk with your doctor.