FSH (Follicle Stimulating Hormone) or follitropin

Follicle Stimulating Hormone – also known as FSH or follitropin – is produced by the pituitary gland and regulates the functions of both the ovaries and testicles. Its low levels can cause infertility in both men and women.

Follicle Stimulating Hormone (or FSH) is one of the gonadotropic hormones (hormones naturally produced by the pituitary gland); the other is luteinizing hormone (or LH).

It is also one of the essential hormones for pubertal development and the function of ovaries in women and testicles in men.

In women, this hormone stimulates the growth of ovarian follicles in the ovary prior to the release of an egg from a follicle at ovulation. It also increases the production of estradiol from the ovaries.

In men, follicle-stimulating hormone acts on the Sertoli cells of the testicles to stimulate sperm production (spermatogenesis).

What does FSH do in women

As the name suggests, FSH stimulates the development and maturation of ovarian follicles in the female reproductive system. It plays an equally important role in the male reproductive system, making the production of sperm possible.

In women, FSH acts directly on the granulosa cells in the ovaries. At the beginning of the menstrual cycle, the levels of FSH in the blood rise. This stimulates the maturation of one of the ovarian follicles, which contains an egg (ovum). As this happens, the follicle begins producing estradiol and its blood levels rise. FSH levels momentarily decrease as estradiol levels rise. Around day 14, however, peak estradiol levels cause a rapid rise in FSH and LH levels. This directly results in ovulation, the release of the now mature egg cell from its follicle. After ovulation, FSH levels drop in response to an increase in progesterone and remain low until the start of the next menstrual cycle.

What does FSH do in humans

In men, FSH acts on the Sertoli cells, which are found in the testicles. These cells are responsible for producing sperm.

Normal values

Similar to other reproductive hormones such as estradiol, LH or progesterone, FSH levels in women fluctuate according to the phase of the menstrual cycle.

Normal values ​​for women are as follows.

  • Days 1-14 (follicular phase): 3.3-11.3 mLU/mL
  • Day ~14 (ovulation): 5.2-20.4 mlU/ml
  • Days 14-28 (luteal phase): 1.8-8.2 mLU/mL

FSH levels are stable in men and do not fluctuate after puberty. The suggested normal range of FSH for men is 1.6 to 11.0 mLU/mL.

FSH basso

Hypogonadotropic hypogonadism is defined as the state with low levels of FSH and sex hormones in the blood. 

In individuals with hypogonadotropic hypogonadism, the pituitary gland does not produce the required amounts of FSH and LH.

For this reason, estradiol and inhibin levels are low in women and follicle maturation is impaired.

On the other hand, low FSH level in males results in lower sperm production.

Low FSH can cause various problems, most notably no or irregular periods in women and infertility in both genders.

If hypogonadotropic hypogonadism affects children or adolescents, it can cause delayed puberty, underdeveloped reproductive organs in both sexes, and absent menstruation in girls.

FSH alto

High FSH levels can be accompanied by low, normal, or high sex hormone levels.

High levels of the FSH hormone usually indicate a problem in the reproductive organs, which produce insufficient sex hormones.

The feedback loop between the gonads, hypothalamus and pituitary gland is consequently disturbed. This state is called hypergonadotropic hypogonadism.

Pituitary adenomas can also cause high FSH levels.

Diagnosing and treating the underlying medical problem causing a high FSH level can help restore its levels to normal.

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform, Maternicity.com.

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