Follicle Stimulating Hormone (FSH)

What is Follicle Stimulating Hormone?

Follicle-stimulating hormone (FSH) is a hormone secreted by the anterior pituitary gland that has important roles in sexual health. It is a gonadotropic hormone that stimulates the growth and activity of the reproductive organs, ovaries in women and testes in men.

FSH role in foetal development

During the second and third trimesters of pregnancy, and the first three and six months after birth, the pituitary gland releases luteinising hormone (LH) and FSH. Both hormones peak during mid-pregnancy as the first ovarian follicle or seminiferous tubule matures in the developing foetus^[1].

FSH role during puberty

FSH levels remain low during childhood until puberty. During puberty, gonadotropin hormone-releasing hormone (GnRH) stimulates the secretion of LH and FSH from the anterior pituitary gland.

In boys, FSH and LH work simultaneously to stimulate the testes to produce testosterone, the hormone responsible for the development of male sex characteristics and sperm production.

In girls, FSH and LH stimulate oestrogen production from the ovaries. Oestrogen is one of the main female sex hormones and it encourages the development of female sex characteristics.

FSH role in the menstrual cycle

In women, FSH and LH control the menstrual cycle. The main role of FSH is to stimulate the development of ovarian follicles and prepare for ovulation.

Ovulation is a phase in the menstrual cycle which occurs around day 14 of a 28-day menstrual cycle. Ovulation is the release of an egg from the ovary.

In the build-up to ovulation, around days six to 14, FSH levels increase and promote the development of ovarian follicles. During days 10 to 14, one of the ovarian follicles becomes dominant. A surge in LH around day 14 causes the dominant follicle to rupture and release the egg. This is ovulation.

Once ovulation has occurred, the ruptured follicle develops into a small ball of cells called the corpus luteum that produces a large amount of progesterone to prepare the womb for pregnancy and stop the production of FSH.

FSH levels then remain low throughout the luteal phase, stopping the development of new follicles, as the body prepares for potential pregnancy. If the egg isn’t fertilised, the corpus luteum breaks down, the menstrual cycle begins again, and FSH levels start to rise^[2].

FSH role in fertility

In women, FSH is critical in regulating the menstrual cycle, triggering the development of ovarian follicles and preparing the eggs for ovulation.

In men, FSH is important for normal sperm production^[3].

Hormonal fluctuations in both men and women, including FSH, can have a detrimental impact on fertility.

Normal FSH Levels

According to the NHS, the normal reference ranges for FSH are:

Data collected from Forth customers shows that FSH levels surge in women at peri- and postmenopausal age. Our results show a slight increase in male FSH levels in men over 60. This is consistent with other findings that state FSH (and LH) levels rise in men as testosterone levels fall^[5].

What levels indicate menopause

Forth data shows that the average FSH levels before menopause are 10.7 IU/L but rise to 60 IU/L after menopause. During menopause and postmenopause, FSH levels continue to increase because of the decline in oestrogen^[6]. The low levels of oestrogen mean the feedback loop which tells the pituitary gland to stop producing FSH is disrupted, so FSH levels continue to rise^[7].

Causes and Symptoms of Low FSH

Several conditions can cause low FSH levels:

1. Hypothalamus dysfunction
   a. Kallman syndrome: an inherited condition that causes puberty delay or absence. It causes a loss of sense of smell. Kallman syndrome means the pituitary gland or hypothalamus does not produce the hormones needed to signal to the sexual organs to produce sex hormones (hypogonadotropic hypogonadism).
2. Pituitary gland disorders
   a. Pituitary gland tumours: Tumours such as benign prolactinomas can cause FSH suppression.
   b. Hypopituitarism: a rare condition which causes the pituitary gland to produce too few hormones including FSH.
   c. Sheehan syndrome: a condition caused after birth when a mother loses lots of blood during delivery. The condition damages the pituitary gland and causes a lack of hormones including FSH^[8].
3. Medications
   a. Hormonal contraception: Sequential pills suppress FSH production throughout the menstrual cycle^[9]. In men, testosterone replacement therapy suppresses FSH production which can cause infertility^[10].
   b. Chemotherapy: Cancer treatments like chemotherapy can reduce FSH levels^[11].
   c. GnRH agonists and antagonists: Although these initially stimulate the secretion of FSH and LH, continuous use has the opposite effect, suppressing LH and FSH.
4. Pregnancy: FSH levels remain very low during pregnancy because the increased levels of oestrogen and progesterone keep them suppressed^[12].
5. Hypothyroidism: An underactive thyroid can lower FSH and LH levels, leading to infertility^[13].

Symptoms of low FSH levels

The symptoms of low FSH levels will depend on the underlying cause but may include:

• Irregular periods

• Impotence in men

• Infertility

• Low libido

• Weight gain or loss^[14]

Causes and Symptoms of High FSH

High FSH levels are usually a side effect of hypogonadism – where the ovaries or testes produce no or low levels of hormones – causing the pituitary gland to release high levels of FSH as it tries to stimulate the gonads to produce more sex hormones.

Some of the main causes of high FSH levels:

1. Menopause

   The natural decline in ovarian function during menopause leads to reduced oestrogen levels and increased FSH levels as the body tries to stimulate the ovaries to function normally.

2. Premature ovarian failure

   Also known as primary ovarian insufficiency, premature ovarian failure is when a woman’s ovaries stop working before the age of 40.

3. Klinefelter syndrome

   a genetic condition where boys are born with an extra X chromosome, causing testicular dysfunction and high FSH levels^[15].

4. Turner syndrome

   a genetic condition that affects females and is characterised by a missing or partially missing X chromosome. The condition causes elevated FSH levels^[16].

5. Polycystic ovary syndrome (PCOS)

   PCOS causes a rise in the LH: FSH ratio. It can also cause elevated FSH levels but is usually associated with high LH levels.

Symptoms of high FSH levels

The symptoms of high FSH levels will often depend on the underlying cause. Here are some of the conditions associated with elevated levels and their symptoms:

How to Check Your FSH Levels

You might be interested in checking your FSH levels if you are experiencing any symptoms associated with reproductive health or fertility.

Testing your FSH levels may help with:

• Understanding why you’re experiencing irregular periods

• Investigating fertility issues or why you might not be able to get pregnant

• Confirming menopause

You can test your FSH levels with Forth using the following tests:

Other tests are available to check your FSH levels, such as over-the-counter menopause tests. These are often urine-based tests, similar to pregnancy tests, measuring the amount of FSH in urine. Because they only measure one hormone, FSH, these tests cannot accurately indicate whether a woman is in perimenopause or menopause^[18].

Instead, tests like our MyFORM® Perimenopause Blood Test map all of the key female sex hormones across the menstrual cycle, providing a much more accurate insight into a woman’s fertility.

Written by Leanne Edermaniger

Based in the UK, Leanne specialises in writing about health, medicine, nutrition, and fitness.

She has over 5 years of experience in writing about health and lifestyle and has a BSc (hons) Biomedical Science and an MSc Science, Communication and Society.