What is FSH?

What is FSH?

4 min read

Follicle-stimulating hormone (or FSH) is just one of the several hormones that affect your body's functions, including the reproductive system. As its name suggests, the main role of FSH is to stimulate the small follicles (the sacs that hold the eggs) early in the menstrual cycle so that one will be recruited and released ahead of ovulation. FSH is also a marker of ovarian reserve (letting you know more about how many eggs you have left) and fewer eggs could mean you’re closer to menopause which marks the end of your reproductive years. For IVF patients, understanding ovarian reserve helps doctors predict how well your ovaries will respond to treatment (in general, more eggs equals more chances to create a viable embryo). Read on to learn more about what FSH is and how it’s measured.

What does FSH do?

For females, FSH is secreted from the pituitary gland and it promotes development in the ovaries (follicular development). It’s associated with quantity—how many eggs—when tested in relation to fertility.

Hormones during the menstrual cycle

FSH rises during the first part of the menstrual cycle and stimulates the development of follicles. As follicles develop, they secrete estrogen, and this increased level of estrogen thickens the endometrium (in preparation for an embryo to implant) and tells the brain to reduce FSH. As a result, one dominant follicle is recruited each cycle (the most sensitive follicle to the decreasing FSH levels), just before ovulation.

As ovarian reserve decreases, FSH levels rise—because more FSH is needed to kick-start follicle development. A higher FSH on day 3 of the menstrual cycle is linked with diminished ovarian reserve, making FSH a marker of egg quantity. 

What is Diminished Ovarian Reserve? →

How is FSH tested?

FSH can be measured in the blood or urine. In both cases, FSH should be tested early in the menstrual cycle, ideally on days 3, 4, or 5 (day 1 being the first full day of bleeding).

What is an FSH blood test?

To get an FSH serum (A.K.A. blood) test, you’ll need a doctor’s requisition for blood work to be done on day 3 of your cycle. The result gives your doctor a helpful data point that can guide your care. Measuring FSH is routinely included in fertility work-ups alongside other ovarian reserve tests like AMH (anti-mullerian hormone; also a blood test) or pelvic ultrasounds (to assess the number of antral follicles) to get a clearer picture of your reproductive health.

What is an FSH urine test?

Measuring FSH at home is possible through urine strips that assess FSH and work similarly to at-home ovulation and pregnancy test kits (think: dipsticks that reveal a line that darkens to indicate results). At-home FSH tests are a screening tool (meaning they aren’t diagnostic and often require more testing to confirm results), but they can be a great way to determine if your FSH is rising, which can flag diminished ovarian reserve. Bird&Be’s Ovarian Reserve Screening Test detects FSH in your urine to suggest normal, elevated, or high FSH. This FDA-approved test has proven to be 99% accurate compared to blood tests, making it an easy and accessible way to make informed and empowered decisions about your fertility. If you find your levels are elevated, you can follow up with a doctor for diagnostic testing (like blood tests and ultrasound) and, if needed, guidance on next steps. You may choose to adjust timelines of when you try to conceive or decide to freeze your eggs.

What is normal FSH?

Fertility doctors consider day-3 FSH levels less than 10 mIU/mL to be normal (note: hormones change throughout the menstrual cycle, but for fertility testing, it’s most helpful to measure FSH at the start of the cycle, A.K.A the follicular phase). A day-3 FSH level greater than 40 mIU/mL is considered in the menopausal range. Though it’s a big range, anywhere between 11 and 39 mIU/mL is considered elevated and worth checking in with your doctor or heading to a fertility clinic if you are hoping to become pregnant (either now or in the future) to plan ahead.  

What is a normal FSH level to get pregnant?

FSH levels less than 10 mIU/mL on cycle day 3 are considered normal. But of course, FSH levels don’t reflect the underlying egg quality or, if you know that you’re ovulating, predict your chance to conceive without intervention. While it’s a good indicator of ovarian reserve, FSH is just one piece of the fertility puzzle, and it alone won’t determine if you can get pregnant. Instead, it provides insight into your timeline (how many eggs you have left), helps with fertility decision-making, and can help predict how responsive your ovaries might be to fertility medications.