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Defining FSH and Why You Test It


FSH (follicle stimulating hormone) is a hormone produced by the pituitary gland. FSH causes follicles — the sacs in your ovaries that contain eggs — to grow. FSH is the primary hormone responsible for producing eggs.

In men, FSH is necessary for sperm production.

When Should You Have FSH Levels Checked?

You would have your FSH levels checked if your menstrual cycle has stopped or become irregular to see if you have entered menopause.

If you are having trouble becoming pregnant, FSH is checked as part of the standard fertility workup.

In men, FSH is checked if sperm counts are low and/or if the female partner is having trouble becoming pregnant.

When Are FSH Levels Checked?

You should have your FSH level checked on day three of your menstrual cycle. This is because FSH starts the ovulation process by getting a follicle growing. The FSH level provides information about how hard your body has to work to get this process started. If your ovarian reserve (how many eggs you have left) is low, your body will have to work much harder and FSH levels will be higher.

What Does the FSH Test Look For?

FSH levels are used to evaluate ovarian reserve, which is how many eggs you have left. It doesn’t provide information about the quality of these eggs, however.

What Do FSH Test Results Mean?

If you are in your late 30s to age 40, high FSH levels are not normal. High FSH levels indicate poor ovarian reserve. In this condition, you may have either relatively few eggs left in the ovaries or impaired development or recruitment of the eggs. Recent research suggests that this condition may be a precursor to premature ovarian failure.

There are also some congenital or genetic conditions that can result in high levels of FSH, such as Turner Syndrome or Congenital Adrenal Hyperplasia. Also, extremely rarely, high FSH levels could be the result of a pituitary tumor.

Low levels of FSH may be associated with polycystic ovary syndrome (PCOS) and disorders of the pituitary gland or hypothalamus.

In men, high levels of FSH may indicate testicular failure. Low levels of FSH may indicate failure of gonadal function.

The bottom line is that abnormally high or low levels of FSH are, unfortunately, an indicator of infertility or decreased fertility in both men and women.

Fertility Treatment and FSH Levels

If your FSH levels are abnormal, the first step is to find out if there is an underlying cause and treat it if possible. In most cases, however, there is not an underlying cause — your body simply isn’t producing the right amounts.

The next step will also be determined by the results of other hormone tests. For example, if FSH is low but estradiol is high, then the estradiol may be artificially suppressing the FSH.

You may be offered a clomiphene challenge test if your FSH level is normal, but you are having trouble getting pregnant. This can help to discover some cases of poor ovulation.

If your FSH levels are normal, then you will probably respond well to ovarian stimulation. As FSH levels rise, you see less response to ovarian simulation. If your FSH levels are very high, you will probably not be given fertility drugs because virtually no response would be expected.

If you are unable to become pregnant or to obtain sufficient eggs for IVF due to FSH levels, you may choose to use a donor egg with IVF.