What Is Significance of FSH Levels?

QuestionWhat Is Significance of FSH Levels?:

“I am looking for information on FSH hormone levels. Mine is prematurely high (12.9-14.5) on Day 2 of my cycle. Why is it tested on Day 2? Does the level fluctuate?”


First, some background: FSH is an acronym for follicle stimulating hormone. FSH is one of several reproductive hormones that our bodies should be producing at certain ranges during certain times in each ovulatory cycle, in order for optimal ovulation to occur. FSH, which is produced by our pituitary gland, does what its name implies — it stimulates follicles to grow. Within our ovaries, follicles are the structures that contain the egg cells.

So given all of the above, FSH is a pretty important hormone to the conception process. A number of things can go wrong in a body that would lead to inadequate production or overproduction of this and other hormones. When the ranges that have been determined as optimal for conception are thrown off one way or another, a problem can result.

An example of how delicate this optimal balance is: While those of us who are learning about infertility tend to worry most about FSH levels that are too high (and I’ll explain why later), it is also the case that too little FSH can hamper conception. Hypothalamic anovulation (or lack of ovulation due to a malfunction of the hypothalamus gland) is a result of too little or no FSH production.

If female infertility is suspected, basic testing of what is called “ovarian reserve” is done. Ovarian reserve refers to a woman’s egg supply, thereby being somewhat predictive of her reproductive capability. Testing a woman’s level of FSH in her blood on the third day (Day 3) of a cycle has been found to be considerably predictive of her fertility within an IVF cycle.

Going back to our more common concern around here, that of too-high FSH levels: according to Dr. Robert Jansen, author of Overcoming Infertility, FSH levels that are high, particularly on more than one occasion, “means that the pituitary gland is trying to overcome — to compensate for — an absence of responsive follicles in the ovaries, which is just what happens naturally at menopause…” Overly abundant FSH is one of the hallmarks of primary or premature ovarian failure, sometimes referred to as early menopause.

How high is too high?

First, you should know that lab values may vary, so you’ll have to talk with your own medical team about the ranges that their lab uses and what they take it to mean. Second, stay aware of things such as possibility of lab error, as well as the fact that FSH (and other hormone) levels can fluctuate as affected by environment, stress, illness, etc. Last, in most cases, one FSH test cannot predict all by itself a woman’s fertility.

Generally, the lower the FSH, the better for fertility. Most docs like to see numbers below 15 mIU/ml.

As far as timing of the test and fluctuation of FSH: it is not necessary for the test to be run on exactly Day 3. Depending on the individual, there should be only slight fluctuation of FSH levels from days 2 through 5. What is important is fluctuation of the hormone levels from cycle to cycle, rather than fluctuations within a given cycle. It is believed that when a woman’s hormones maintain relative sameness over several cycles, she is more apt to be producing high quality eggs.

Some experts now believe that a woman’s fertility is only as good as her highest FSH level. Even if her hormones return to normal levels after measuring high FSH in the previous cycle, her fertility is diminished, at least during that follow-up cycle.

The question of FSH and other ovarian reserve testing is one of great concern for most women undergoing evaluation for conception difficulties. It is important to understand as fully as possible the entire hormonal picture, how the body’s endocrine system and responses lead to fertility or infertility, rather than relying on numerical results from one test. There are many more ways (in addition to FSH testing) to determine ovarian reserve, and women should approach the possible diagnosis of premature ovarian failure with educated skepticism.

For more information on FSH and testing for ovarian reserve, see the following:

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