What the FSH blood test can tell you

I had never heard about the FSH blood test, nor about what FSH is. One day I went to see my doctor (I very rarely go to "my" doctor, maybe once a year or less). I told her I was considering getting pregnant and I wanted to ask for some advice, whether I had to check anything in particular about my health, or do anything special before starting.

She saw my age (I won't go into details, but it was above what most doctors consider the "right age" for a woman to get pregnant), asked me whether I had regular periods, (I said yes, always had), whether I smoked (no), drank alcohol (no), measured my pressure (OK, 130).

Everything seemed fine, so she agreed that, indeed, there should be no problems, I should get pregnant, recommeded to take folic acid, 400 mg every day, and ordered me to do this FSH blood test.

She didn't explain me anything else, so I went home and started researching, I wanted to know, what does FSH mean?

What does FSH mean?

So I learnt that FSH means "follicle stimulating hormone". It is a hormone that, in women, stimulates follicles in the ovaries to produce and release an egg every month. Also men produce FSH but of course it has a different function.

How FSH works

The follicle-stimulating hormon is an indicator of the functionality of the ovaries, how well they work or not.

When everything works normally, the pituitary gland (thyroid) produces a small amount of this hormone to stimulate the ovary follicles to release an egg every month.
When ovaries do not respond to the stimulation, the pituitary gland (thyroid) has to produce a greater amount of FSH to obtain the same result, the release of an egg every month.

Therefore, high FSH levels are considered an indicator that a woman's ovaries are not working very well and, generally, that she is approaching menopause.

FSH levels change during the cycle

Every month, during a woman's cycle the level of FSH changes. At the beginning the level is low, then it increases to stimulate the ovary to release an egg. The highest level of FSH occurs just before ovulation, around the middle of the cycle. That's why the FSH blood test is usually done between day 2 to 5 of the cycle, to avoid a "false" high level. It's often referred to as "day 3 FSH test".

Normal FSH levels

What are considered normal FSH levels vary a lot depending on the labs that do the FSH blood test. Anyway, together with the FSH test results, the lab will provide their own reference ranges.

Here is an example of normal FSH levels ranges for women, according to the US National Institutes of Health's website:

  • Before puberty: 0 - 4.0 mIU/ml
  • During puberty: 0.3 - 10.0 mIU/ml
  • Women who are menstruating: 4.7 - 21.5 mIU/ml
  • Postmenopausal: 25.8 - 134.8 mIU/ml

So a high FSH level depends on age but not only. There are young women with high FSH levels.

When I received my FSH blood test results I was happy to learn that my FSH level was low, I mean, right for a woman of fertile age. In a way, it was telling me that I am young, (what I've always thought)!

My FSH level was 4.6 IU/l and this lab's normal FSH level range was 1.5-33 (quite different from the above ranges).

Infertility and high FSH

Often infertility and high FSH levels go together and high FSH levels indicate that there will problems when trying to conceive, but I've read of women with high FSH who have conceived, so there is hope. I've read that FSH levels begin to rise more than a decade before menopause, good to know.

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