AMH test: what your AMH value does and does not say

What is AMH? The AMH hormone, in full anti-Müllerian hormone, is made by the cells around the smallest follicles in your ovaries. A follicle is the little sac in which an egg can mature. You are born with a fixed stock of those follicles, and that stock gets smaller throughout your life. The more small follicles still sitting in your ovaries right now, the more AMH there is to measure in your blood, and the lab reports that amount in micrograms per litre (µg/l).

That is why AMH is used as a measure of your ovarian reserve. There is nothing complicated behind that word: it is simply an estimate of how many follicles you have left. A gynaecologist can also literally count those small sacs on an ultrasound, and the answer comes out roughly the same; an AMH blood test is the version of that count with no ultrasound attached.

The reason the test is so easy to schedule lies in where the hormone comes from. The smallest follicles grow without your pituitary driving them. FSH, LH and oestradiol are driven by your pituitary and therefore swing strongly with your cycle, which is why they belong around day three. AMH barely swings at all, so you can have your blood drawn whenever it suits you, even if your cycle is irregular or you have no idea which day you are on.

What AMH does not do is look at the quality of your eggs. It is a headcount and not an inspection. Egg quality is mainly related to your age and cannot be measured with any blood test, so a good-looking AMH value is not a guarantee and a low value is not a verdict.

The laboratory that runs the test uses one range for adult women, 1.07 to 6.32 µg/l, and that range takes no account of your age. µg/l is exactly the same as ng/ml, the unit you meet in English-language articles; if your laboratory works in pmol/l, 1 µg/l corresponds to roughly 7.1 pmol/l. Never put your AMH value next to a friend's from a different laboratory, because the assays are not standardised and give different numbers for the same blood.

More expectation hangs on AMH than the number can carry. Search online and you quickly read that an AMH blood test shows how much time you have left, and that is not true; you are better off knowing it before a result lands in your inbox.

Start with the range on your result. The laboratory prints one range for adult women, 1.07 to 6.32 µg/l, and it is not adjusted for age, while AMH falls throughout your life. In women aged 20 to 24 the median sits around 4.0 µg/l, at 30 to 34 around 2.8, at 35 to 39 around 2.0 and at 40 to 44 around 0.9; those are the age bands of the assay the lab uses, as orientation and not as a limit. The same 1.2 µg/l is therefore strikingly low at 24 and above average at 41. Always read your AMH value alongside your age rather than against that one range alone.

The second misconception is the biggest one. A low AMH value does not mean you cannot get pregnant. In women without a fertility problem AMH is barely related to the chance of conceiving within a year: research among women who had only just started trying (Steiner, JAMA 2017) showed that a low value did not meaningfully reduce that chance. Which makes sense, because as long as your cycle runs and you ovulate, one egg at a time is all you need. AMH is a number to plan with and not a countdown clock.

The third misconception: AMH does not predict when you will reach menopause. The value falls as menopause approaches, but the difference between women of the same age is so large that no year can be derived from it. Any website or test that promises you an age for your menopause on the basis of AMH is promising something your blood does not know.

So what is an AMH test actually good for? Mostly for planning. Doctors use the value to estimate how your ovaries respond to hormonal stimulation, for example in IVF or when freezing eggs: how many eggs a treatment is likely to yield, and what dose makes sense. Beyond that, a clearly low value, together with your age and your cycle, can be a reason to talk to your GP or gynaecologist sooner about wanting children. That conversation is the real yield of this test.

When can you test AMH? Whenever you like. An AMH test may be done on any cycle day, you do not need to fast and you do not need to count days; even if your cycle is irregular or absent altogether, the result stays usable. In that respect AMH differs from almost every other female hormone.

The more interesting question is whether the test gives you anything. For most women with no complaints and no concrete plans for children, an AMH value does not: you get back a number that leads to no action, and sometimes a scare that rests on nothing. Testing is worthwhile when conceiving is taking longer than you expected, when you are thinking about freezing eggs, when your cycle has been irregular or absent for months, and before or after ovarian surgery.

With an irregular cycle your GP rarely looks at AMH alone. An underactive thyroid or a raised prolactin can throw a cycle off just as easily, so TSH and prolactin often go along in the same blood draw.

Do you use the pill, an implant or a ring? Always flag it with your result. Combined hormonal contraception pushes AMH down by roughly a quarter on average, so your result then underestimates your true reserve; the effect is reversible and after stopping the value usually recovers within a few months. Never stop your contraception on your own initiative to have a blood value measured, but discuss it with your GP first.

And how fast does your AMH value actually fall? Gradually, and fastest after thirty. In the age bands of the assay the lab uses the median sits at roughly 3.3 µg/l at 25 to 29, roughly 2.0 at 35 to 39 and roughly 0.9 at 40 to 44. The spread within any age is enormous and these figures come from one specific assay, so use them to place a result and not to give yourself a score.