Normal levels of follicle stimulating hormone (FSH) depend on the age and gender of the person in question. According to MedlinePlus, normal FSH levels for a female are 4 milli international units per milliliter (mIU/ml) or less before puberty and between 0.3 and 10 mIU/ml during puberty. During a woman's years of menstruation, levels between 4.7 and 21.5 mIU/ml are usually considered normal while a post-menopausal woman may have normal FSH levels between 25.8 and 134.8 mIU/ml. A male's normal FSH levels are usually 5 mIU/ml or less before puberty, between 0.3 and 10 mIU/ml during puberty, and between 1.5 and 12.4 mIU/ml during adulthood.
FSH is an important hormone that plays a critical role in reproduction. In women, normal levels are crucial for egg production as well as for proper levels of another hormone called estradiol. In men, normal levels of this hormone are important for the production of sperm. There is some variation in normal levels, however, and doctors usually consider a range of normal values rather than pinpointing a single number. For example, one woman with an FSH of 7 may be told her levels are normal, even though another woman with an FSH of 5 has been told her levels are normal — sometimes normal values can differ slightly from one laboratory to another as well.
Often, FSH level discussions focus on women since many doctors use these values as a measurement of a woman's fertility. In such cases, a woman may be told her FSH is high, even if it is within the normal range. For example, if a woman has an FSH of 10, many doctors will tell her it is high, despite the fact that levels under 21.5 are within the normal range for women who have not reached menopause. This is because at 10 or above, women are said to have diminished ovarian reserve, which may make it harder for them to become pregnant. Levels that are in the high teens or higher may even mean a woman is close to menopause.
It is important to note that having normal FSH levels doesn't necessarily mean an individual is fertile, and high levels don't always mean a woman cannot conceive easily. There are other hormones that play a role in reproduction, and these, along with other factors, may influence her success as well. Additionally, there are some medications that might affect the accuracy of FSH testing, which is accomplished by drawing blood.