What is FSH (Follicle Stimulating Hormone)?

FSH: Definition and Why Follicle Stimulating Hormone is Important for Female Fertility

Follicle stimulating hormone (FSH) is a gonadotropin produced in the pituitary gland that aids in the production of eggs in women and sperm in men. In women, FSH plays an important role in the growth of follicles and the maturation of oocytes (eggs). The number and quality of eggs a woman can produce is a key factor in determining whether she can conceive with her own eggs, or will need to use donor eggs. Along with luteinizing hormone (LH), follicle stimulating hormone is also used in fertility treatments like IVF to encourage multiple eggs to develop in a single cycle. FSH levels naturally rise with advancing age. Counterintuitively, high FSH levels in women is not a good thing for fertility, as elevated FSH levels indicate low ovarian reserve, associated with low pregnancy chances.

FSH Function: Promoter of Follicle Growth in the Ovaries

Stages of oocyte maturation

FSH promotes oocyte maturation

FSH functions as a promoter of oocyte development in the last 2 weeks of this months-long process leading up to egg retrieval in an IVF cycle.


Women are born with immature eggs that remain in the “resting” state in the ovaries. These eggs are contained in fluid-filled pouches called follicles. Every month, a whole cohort of these resting, immature eggs are recruited into folliculogenesis, a process in which immature eggs mature into ovulation-ready stage. Each month, through this process of folliculogenesis, a woman usually produces one follicle with one mature egg inside. During the follicular phase of the menstrual cycle, which begins after the last day of her menstrual period and continues until ovulation (usually around day 10-18), the follicle sac will grow and the egg within that pouch will mature. When the follicle and egg reach full maturity, the follicle will burst, releasing the egg to move into the fallopian tubes for fertilization. This is part of the process known as ovulation.

Follicle stimulating hormone plays a number of roles in folliculogenesis. It encourages the granulosa cells, which are the cells that surround and support the eggs; it recruits multiple immature eggs into the maturation process; FSH also promotes the development of antral follicles (more developed follicles closer to being ready for ovulation). Because of the many roles it plays during folliculogenesis, FSH affects the number and quality of follicles and eggs a woman produces during a given cycle. In IVF cycles, FSH is administered during the ovarian stimulation phase to encourage multiple follicles to develop and mature so that many eggs are available for retrieval and fertilization.

The number and quality of eggs available for fertilization obviously have implications on a woman’s chances of pregnancy whether with or without fertility treatment. Along with anti-Mullerian hormone levels, FSH function plays an important role in all of these outcomes, and FSH levels are thus used as an important indicator of a woman’s fertility.

FSH Hormone Function is Used to Determine a Woman’s Reproductive Capacity

When a couple encounters difficulty conceiving, one of the first things a reproductive endocrinologist does is hormonal testing, which usually includes a follicle stimulating hormone test. This test is usually performed around day 2 or 3 of a woman’s menstrual cycle, when FSH reaches its highest level. The test measures the amount of FSH in the woman’s blood.

Based on the results of the FSH testing and many other factors, CHR physicians develop a diagnostic and treatment protocol to better understand the causes behind a patient’s abnormal FSH levels, as well as what can be done to treat the symptoms and ultimately help her conceive with her own eggs.

Don’t Delay Fertility Treatment Waiting for FSH Function to Improve

Elevated FSH causes difficulty conceiving, but it’s treatable. Because FSH levels increase with age, it isn’t a good idea to wait -- time is of the essence when treating age-related infertility in women.

Contact CHR for A Consultation About FSH Hormone Function

If you have any questions about FSH, FSH function, or FSH in females, contact us to schedule an individualized consultation. Watch more videos on FSH and infertility.

infertility physician

Norbert Gleicher, MD, FACOG, FACS

Norbert Gleicher, MD, leads CHR’s clinical and research efforts as Medical Director and Chief Scientist. A world-renowned reproductive endocrinologist, Dr. Gleicher has published hundreds of peer-reviewed papers and lectured globally while keeping an active clinical career focused on ovarian aging, immunological issues and other difficult cases of infertility.

Follow Dr. Norbert Gleicher on Google+ Center for Human Reproduction: Follow us on Google+. IVF center with best fertility options for each infertility patient. or LinkedIn Center for Human Reproduction: Follow us on Google+. IVF center with best fertility options for each infertility patient.

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Last Updated: May 20, 2019

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