How Follicle Stimulating Hormone (FSH) Helps Fertility Treatments

illustration of ovulation

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Follicle-stimulating hormone, or FSH, is a hormone released from the pituitary gland in the brain that stimulates an egg follicle to grow each month as part of the menstrual cycle. Women with PCOS often do not ovulate on a monthly basis due to low FSH levels.

If your doctor suspects you may have PCOS, he or she will order blood work for FSH along with other hormone levels prior to diagnosis. Older women tend to have elevated blood levels of FSH, which indicate ovarian maturing. This is because greater amounts of the hormone are required for the ovary to recruit and stimulate an egg follicle.

FSH Levels During Your Cycle

Throughout your menstrual cycle, levels of FSH vary. Doctors often test FSH levels on day 3 of your cycle. These are considered your baseline levels. FSH is part of a complex dance of hormones that includes luteinizing hormone (LH), estradiol, and gonadotropin-releasing hormone (GnRH). FSH stimulates an immature follicle to grow. Once it is grown, it releases estradiol, which signals the release of GnRH and LH, prompting ovulation.

Prior to ovulation, FSH levels will peak, signaling the ovary to release an egg. Once ovulation has occurred, the levels will return to or dip slightly below the baseline.

Normal baseline FSH levels are between 4.7 and 21.5 mIU/ml in women who are menstruating.

Certain medications, such as birth control pills, clomiphene, digitalis, and levodopa, can alter the test results. Your doctor will instruct you to stop taking those drugs before taking an FSH test. In the case of hormonal birth control, it should be stopped at least four weeks prior to taking the test.

FSH and Pregnancy Planning

Since women with PCOS have low FSH levels and, therefore do not ovulate regularly, she will typically see a fertility specialist or reproductive endocrinology for help in getting pregnant when the time is right.

These specialists, known as reproductive endocrinologists, will use a variety of drugs and hormones to promote ovulation and stimulate secretion of the sex hormones in women with fertility problems. FSH is one of the hormones they regularly turn to.

Reproductive endocrinologists will use a synthetic form of FSH (such as Gonal-f, Follistim, or Bravelle) to stimulate the ovaries to produce egg follicles for either intrauterine insemination (IUI) or in vitro fertilization (IVF).

Many women are often anxious to hear that shots are needed to stimulate ovulation. While injections may be uncomfortable, it's important to keep your eyes on the bigger picture—having a baby.

FSH and Ovarian Reserve

In women who want to become pregnant later in life, FSH levels are used to test ovarian reserve (the number and quality of eggs a woman has left). Your doctor will have blood work drawn on the third day of your menstrual cycle. The results are typically available within 24 hours depending on the lab.

Based on the results of the lab studies, a fertility specialist will be able to estimate your likelihood of getting pregnant even if you are approaching menopause.

Baseline FSH levels will increase as women enter perimenopause, indicating a decreasing number of oocytes (eggs). Perimenopause lasts four years on average and ends when a woman has not had a period in 12 months.

At that point, menopause begins. FSH levels at menopause are consistently elevated to 30 mIU/mL and above.

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