Follicle stimulating hormone (FSH) is produced by the pituitary gland. It impacts the course of menstrual cycle and stimulates ovulation. Since FSH is responsible for the proper functioning of the reproductive system in women, determining its level is one of the basic tests for the diagnostics of causes of infertility.
The FSH test is a test of concentration of FSH gonadotropin, or foliculotropin, produced by the pituitary gland.
- In women, the blood FSH test is performed to assess the ovarian reserve, as well as to diagnose polycystic ovary syndrome or to diagnose the causes of menstrual disorders, such as irregular menstruation or intermenstrual bleeding.
- In men, a FSH test is performed to find the cause of low sperm levels in semen (FSH stimulates the testicles to produce sperm cells).
How to prepare for a FSH test?
The follicle stimulating hormone level is measured on the basis of a blood sample examination. The test should be performed between the 1st and the 5th day of the cycle (in the early follicular phase). Depending on the reason for the test, the physician may recommend that it should be performed on a particular day of the cycle. As part of the preparation for the FSH hormone test, it may be necessary to discontinue some drugs (even four weeks before blood is taken for analysis), so the patient should inform his or her physician about all the drugs he or she is taking before the test.
The test result may also be affected by the presence of a radioactive marker, e.g. after a thyroid gland or bone examination. You should also inform your physician about this having undergone such diagnostics.
Why should FSH be tested in parallel with oestradiol?
FSH should be tested in parallel with oestradiol, since FSH is subject to negative oestradiol feedback effect. This means that FSH secreted by the pituitary gland affects the production of oestradiol by the ovaries, which in turn reduces FSH secretion by the pituitary gland (the effect inhibits the cause). It may happen that a low FSH value is due to high concentrations of oestradiol produced by the functional ovarian cyst.
FSH normal levels in women
- in the follicular phase - below 12 IU/L,
- in the ovulation phase - from 20 to 90 IU/L,
- in the luteal phase - below 10 IU/L,
- during the menopause - from 40 to 250 IU/L (FSH concentration increases after the menopause),
- during pregnancy - trace concentration.
FSH normal levels in men
- after puberty- from 4 to 25 IU/L.
What could a FSH level out of the range of normal mean?
Too high FSH
The presence of high value of gonadotropins (FSH, LH), with simultaneous low serum oestradiol concentration is typical for the menopause period, which on average occurs in the females of white race at the age of 51-54. The occurrence of symptoms typical of menopause under forty years of age, with a simultaneous increase in the FSH value determined at least twice (at an interval of more than one month) and an indeterminable serum AMH value is typical of premature ovarian failure/ovarian insufficiency (POF/POI). The prevalence of POF/POI is estimated to be between 1% and 2% of women at the reproductive age. In men, too high FHS level can mean testicular failure, testicular damage, e.g. through infectious factors impeding sperm production, as well as primary hypogonadism (diagnosed in Klinefelter syndrome).
Too low FSH
Reduced FSH, both in women and men, is associated with pituitary and/or hypothalamic insufficiency.
FSH and hormone stimulation
FSH is an indirect marker of the ovarian reserve and allows for the evaluation of the ovarian response to the stimulation with exogenous FSH (follicle stimulating hormone introduced into the body as an external pharmacological preparation). It has been traditionally assumed that the serum FSH value at day 2-3 of the cycle above 15 IU/L is treated as an indication of bad response to stimulation and is the basis for excluding the patient from further hormone stimulation. Because it may mean no response to exogenous FSH, i.e. no follicle growth in the ovary.
*** Medical consultation: M.D. Jarosław Kaczyński, gynaecologist-obstetrician and endocrinologist, physician treating couples at InviMed in Warsaw. One of the precursors of oncofertility treatments conducted in cooperation with the team of Bielański Hospital.