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Follicle Stimulating Hormone (FSH) is produced in the pituitary gland and is important for women in the production of eggs by the ovaries and for men for men in the production of sperm.

In the first half of the menstrual cycle in women, FSH stimulates the enlargement of follicles within the ovaries. Each of these follicles will help to increase oestradiol levels. One follicle will become dominant and will be released by the ovary (ovulation), after which follicle stimulating hormone levels drop during the second half of the menstrual cycle.

In men, FSH acts on the seminiferous tubules of the testicles where they stimulate immature sperm cells to develop into mature sperm.

What might a low result mean?

In women low levels can signal that you are not ovulating or are pregnant. It can also be caused by use of oestrogen-containing contraceptives or hormone replacement therapy.

Low levels of follicle stimulating hormone in men can be a sign of underlying problems with the pituitary gland which can impact upon sperm production. Low FSH also be caused by the use of medications which contain testosterone or other androgens.

What might a high result mean?

Levels of FSH rise in women as egg production declines, so it may be used in certain circumstances to assess the likelihood of whether a woman is going through the menopause.

The National Institute for Health & Care Excellence (NICE) recommend that FSH testing is only considered to diagnose menopause in women aged 40-45 with menopausal symptoms (including a change in their menstrual cycle) or in women under the age of 40 in whom menopause is suspected. 

Due to significant fluctuation in FSH levels around the time of menopause, there is a chance that this test may show normal pre-menopause levels of FSH in someone who is going through, or has been through, the menopause.

A high FSH level in a man may mean the testicles are not functioning correctly. This can be caused by damage to the testicles, increasing age, alcohol problems, diabetes and rarely by a tumour of the pituitary gland.