In women, FSH plays a key role in the growth and development of follicles, which are small sacs in the ovaries that contain immature eggs. FSH levels rise at the start of the menstrual cycle, which triggers follicle growth and estrogen production. As estrogen levels increase, the follicles grow larger, and one dominant follicle will release a mature egg during ovulation.

In men, FSH stimulates sperm production in the testes. High FSH levels in men can indicate there might be testes issues, such as damage from chemotherapy or radiation, genetic disorders, or hormonal imbalances.

Abnormal FSH levels in women can be a sign of various conditions such as hypothalamic amenorrhea (HA), premature ovarian failure (POF), or primary ovarian insufficiency (POI). In men, abnormal FSH levels can indicate conditions such as Klinefelter syndrome, testicular failure, or a pituitary gland problem.

It is important to note that FSH levels can vary throughout the menstrual cycle and can be affected by various factors, such as age, stress, and certain medications. Therefore, FSH levels in women should be interpreted in the context of time of cycle at which the FSH level is checked, an individual’s medical history, and other hormone levels.