What is FSH (follicle stimulating hormone)?

26 Aug What is FSH (follicle stimulating hormone)?

FSH, or follicle stimulating hormone, is the engine room of your reproductive system. It’s also the hormone that couples trying to conceive worry about the most. Fertility patients routinely approach the FSH test with trepidation.

Fuelled by horror stories and misinformation online, many of us have been led to believe that our future pregnancy chances hinge exclusively on the numbers that come back from the lab. Will they fall within the ‘right’ range? Is it game over? Interpreting FSH numbers can be tricky and there’s room for misunderstanding and confusion. Stories abound of inadequate advice.

What is FSH? Like LH, its close relative, it’s quite a complex hormone. Centrally controlled by the pituitary gland, FSH manages reproductive cells – in both men and women. In women, it helps regulate menstrual cycles. It’s also instrumental in the production, growth and maturing of follicles in the ovaries. As women near ovulation, FSH levels peak. A good-quality egg effectively reduces your FSH.

So why take the FSH test? Because your fertility consultant wants to know all about your ovarian reserve – how many eggs you have. An FSH test can also confirm if you’ve had the menopause (lots of women contemplate fertility treatment in their forties and early fifties, so this is relevant). It can also reveal other ovarian conditions.

Your FSH result, together with fertility tests like TSH and AMH (the latter is even better at addressing ovarian response), can help you and your doctor decide whether or not to proceed with natural or assisted conception. If the verdict’s IVF, you’ll need to discuss which fertility treatment is best (e.g. whether donor eggs would be better than IVF with your own eggs). And if, when and what medication supplementation may be needed. A normal FSH reading means you’ll probably respond well to ovarian stimulation.

A normal FSH level? It depends on your age, general health and when you take the test. IVF patients, for example, should schedule a basal FSH test within the first three days of their cycle to see if the hormone is sluggish, working too hard or coasting nicely.

An abnormal result isn’t necessarily a barrier to fertility. But broad rules apply. In the follicular phase, a result of no more than 12.5 IU/L is usually considered acceptable. Any more than that and low ovarian reserve, or the menopause, may be on the cards, reducing your chances of achieving a pregnancy. An unduly low result in the same phase (less than 3.5 IU/L) may mean that eggs are not being produced at all. It may also point to stress, PCOS, a pituitary or hypothalamus problem or low body weight.

Mid-cycle, the reference range is 4.7 to 21.5. In the luteal phase, it’s 1.7 to 7.7.  A post-menopause reading can stretch from 25.8 to 134.8.

But remember: an older woman can have poor ovarian reserve with a normal FSH level. And a higher-than-average FSH score in a 30-year-old isn’t as unpromising as a similar FSH level in a 40-year-old, in terms of conception chances. Also, fertility medication can deal with one FSH problem but not another.

In summary, and very generally, high FSH is bad and low FSH is good. But you’ll need to factor in the fluctuations in readings linked to age and other health issues, plus your other fertility tests and procedures. As such, an FSH test is a fairly reliable, though not conclusive, road map of your fertility future. Get it done.