Follicle Stimulating Hormone (FSH) in Serum/Plasma

Follicle Stimulating Hormone (FSH) is a hormone made by the pituitary gland, a small gland located at the base of the brain. In women, FSH helps control the menstrual cycle and stimulates the ovaries to produce eggs. In men, it plays an important role in sperm production. Measuring the level of FSH in your blood can help your doctor understand how well your reproductive system is working.

FSH is a hormone produced by the pituitary gland, a small organ at the base of your brain. It works with another hormone, luteinizing hormone (LH), to regulate the menstrual cycle in women and sperm production in men. In women, FSH helps stimulate the growth of follicles (small sacs containing an egg) in the ovaries. In men, it supports the production of sperm.

Your doctor may order an FSH test if you are having trouble getting pregnant, if your menstrual periods are irregular or have stopped, or if you are having symptoms of menopause. In men, the test may be used to help evaluate a low sperm count or a possible problem with the pituitary gland. It can also be used to check how well fertility treatments are working.

Doctors may order an FSH test to check for hormonal imbalances, especially if you’re experiencing infertility, irregular periods, low libido, or other reproductive concerns. It can also help diagnose conditions like polycystic ovary syndrome (PCOS), ovarian insufficiency, or hypogonadism in men.

For women, the timing of an FSH test often depends on the menstrual cycle, and your doctor may ask you to have your blood drawn on a specific day, commonly around day three. The test may also be done when symptoms such as hot flashes, night sweats, or missed periods suggest hormonal changes. Men and children can usually be tested at any time.

FSH levels can fluctuate throughout the menstrual cycle, so timing matters. In women, tests are often taken during the early follicular phase (around day 2–5 of the cycle) or mid-luteal phase (around day 21). In men, tests are usually done at any time, though levels may vary slightly with stress or illness.

In most cases, no special preparation is needed for an FSH blood test, and you can eat and drink as usual before your appointment. Tell your doctor about any medicines, supplements, or hormone therapies you are taking, because some drugs can affect your results. If you are a woman, your doctor may schedule the test on a particular day of your menstrual cycle to make the results easier to interpret.

No special preparation is needed for most FSH tests, but your doctor may advise fasting for 8–12 hours before drawing blood. Avoid strenuous exercise or alcohol 24 hours before the test. If you’re taking medications that affect hormones, let your doctor know.