Follicle-stimulating hormone (FSH) is released by the pituitary gland in both men in women. The role of FSH in women is different from its role in men, because it controls the menstrual cycle in females. The amount of FSH changes during the cycle and is usually highest just before ovulation occurs. This hormone works in conjunction with luteinizing hormone (LH) to release the right amount of estrogen and progesterone throughout the cycle, so an imbalance of either hormone can result in infertility or menstrual problems. Thus, the amount of FSH in women is usually tested before diagnosing early or delayed puberty, menopause or infertility.
Both FSH and LH are produced by the anterior pituitary, and both are necessary for the menstrual cycle to continue normally. The job of FSH in women is to encourage the eggs in the ovaries to mature in time for ovulation, and the job of LH is to stimulate the ovaries to release progesterone and estrogen. The levels of both hormones increase just before ovulation, which usually takes place in the middle of the menstrual cycle. The levels of FSH in women also increase during menopause, because more of this hormone is necessary in order to ripen the eggs each month.
In some cases, though, high levels of FSH indicate issues other than the natural state of menopause. For example, primary ovarian failure is often signaled by high FSH and LH levels, which might lead to infrequent or even absent ovulation, making it difficult to conceive without medical intervention. High levels of FSH in children might be a result of early puberty, especially when paired with the sudden appearance of menstruation, breasts and pubic hair. Low levels of FSH, on the other hand, often indicate secondary ovarian failure, usually caused by a problem in the pituitary gland or hypothalamus. A low level of FSH in children or teenagers, however, can signal delayed onset of puberty.
Women who are experiencing abnormal menstrual cycles or having trouble conceiving might choose to have their level of FSH tested, because this type of screening can examine the egg supply in their ovaries. In most cases, the ideal day for an FSH test is the third day of the menstrual cycle, at which point a medical professional will draw a sample of blood from the arm and have it tested. The results will be compared to the expected level of FSH in women, taking the age and amount of sexual development into consideration. Other tests might also be offered to determine the levels of LH, estrogen and progesterone, allowing a diagnosis and treatment plan to be developed.