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This test measures the level of follicle stimulating hormone (FSH) in your blood. FSH is made in the pituitary gland and plays an important role in sexual development and function. The test is used to assess fertility and pituitary disorders in men and women. 

In women, FSH helps control the menstrual cycle and the production of eggs by the ovaries. Its level varies throughout the menstrual cycle and is highest just before ovulation when an egg is released. This is known as ovulation. FSH testing is used to investigate irregular menstrual periods or confirm menopause. 

In men, FSH stimulates testicular growth and helps create and maintain normal sperm count. The test is used to find out if there is a problem with the testicles or what may be the cause of a low sperm count. It is also often used to investigate early or delayed puberty.

What is being tested?

Follicle-stimulating hormone (FSH) is made by the pituitary gland in the brain. Control of FSH production is a complex system involving hormones produced by the gonads (ovaries or testes), the pituitary gland and the hypothalamus, such as gonadotrophin-releasing hormone (GnRH).

In women, FSH stimulates the growth and development of ovarian follicles (eggs) during the follicular phase of the menstrual cycle. This cycle is divided into two phases, the follicular and the luteal, by a mid-cycle surge of FSH and luteinising hormone (LH). Ovulation (release of the egg from the ovary) occurs shortly after this mid-cycle surge of hormones. During the follicular phase, FSH initiates the production of oestradiol by the follicle and the two hormones work together in the further development of the egg follicle. During the luteal phase, FSH stimulates the production of progesterone. Both oestradiol and progesterone help the pituitary control the amount of FSH produced. At the time of menopause, the ovaries stop functioning and FSH levels rise.

In men, FSH stimulates the testes to produce mature sperm. FSH levels are relatively constant in men after puberty.

How is it used?

Follicle stimulating hormone (FSH) is often used in conjunction with other tests (LH, testosterone, oestradiol and progesterone) in the investigation of infertility in both men and women. FSH levels are also useful in the investigation of menstrual irregularities (irregular periods) and to aid in the diagnosis of pituitary gland disorders. In children, FSH and LH are used to diagnose delayed or precocious (early) puberty.

When is it requested?

In women and men, FSH and LH are requested as part of the investigation of infertility and pituitary gland disorders. FSH may also be used to determine if a woman has reached the menopause. FSH levels also help to determine the reason a man has a low sperm count. In children, FSH and LH may be requested when a boy or girl does not appear to be entering puberty at an appropriate age (either too late or too soon).

What does the result mean?

In women, FSH and LH levels can help to tell the difference between primary ovarian failure (failure of the ovaries themselves) and secondary ovarian failure (failure of the ovaries due to disorders of either the pituitary gland or the hypothalamus in the brain). Increased levels of FSH and LH are consistent with primary ovarian failure. Some causes of primary ovarian failure are listed below.

Developmental defects:

  • Ovarian agenesis (failure to develop ovaries)
  • Chromosomal abnormality, such as Turner’s syndrome
  • Ovarian steroidogenesis defect, such as 17 alpha hydroxylase deficiency

Premature ovarian failure due to:

  • Radiation therapy
  • Chemotherapy
  • Autoimmune disease

Chronic anovulation (failure to ovulate) due to:

  • Polycystic ovary syndrome (PCOS)
  • Adrenal disease
  • Thyroid disease
  • Ovarian tumour

When a woman enters the menopause and her ovaries stop working, FSH levels will rise.

Low levels of FSH and LH are consistent with secondary ovarian failure due to a pituitary or hypothalamic problem.

In men, high FSH levels are due to primary testicular failure. This can be due to developmental defects in testicular growth or to testicular injury, as indicated below.

Developmental defects:

  • Gonadal agenesis (failure to develop testes)
  • Chromosomal abnormality, such as Klinefelters syndrome
  • Testicular failure:
  • Viral infection (mumps)
  • Trauma
  • Radiation therapy
  • Chemotherapy
  • Autoimmune disease
  • Germ cell tumour

Low levels of FSH are consistent with pituitary or hypothalamic disorders.

In young children, high levels of FSH and LH and development of secondary sexual characteristics at an unusually young age are an indication of precocious (early) puberty. This is much more common in girls than in boys.

Is there anything else I should know?

FSH results can be increased with use of certain drugs, such as cimetidine, clomiphene and naloxone. FSH results can decrease with oral contraceptives (the pill), phenothiazines and certain hormone treatments.

Common questions

  • I’m having a hard time getting pregnant. What tests do I need?

The basic test for infertility is measurement of progesterone to check that ovulation is occurring. Other tests for infertility include FSH and LH and other blood tests to assess your reproductive hormone levels. A post-coital test may be carried out where the cervical mucus is examined 2-8 hours after intercourse to check if the sperm are surviving in it. A hysterosalpingogram (image of fallopian tubes) may be done to see whether your fallopian tubes are blocked. Your partner may be asked to give a specimen of semen for analysis.

  • I am a young woman, but now I am growing facial hair and still have no regular period. What’s wrong with me?

You may have polycystic ovary syndrome (PCOS), a hormonal problem seen in 7-10% of women and a major cause of infertility. With this condition, ovaries may become larger because of cysts that form in them. Women with PCOS also may have high levels of testosterone and do not ovulate normally. You may need to undergo several laboratory tests, including FSH, LH and testosterone, to make sure that PCOS is the condition causing your symptoms. A combination of medications and hormone therapy may help your symptoms.

  • Why would a man need a test for female hormones?

Men also produce FSH and LH in their bodies, and these hormone levels are important for male reproduction too. In men, FSH stimulates the testes to produce sperm just as in women FSH stimulates the ovaries to produce eggs. In men, LH can be measured to investigate the cause of a low testosterone.

Last Updated: Thursday, 1st June 2023

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