Low AMH: what it really means for your fertility

Of all the results we are asked to explain, AMH is probably the one that causes the most worry. Someone has a blood test, often as part of a fertility MOT or before IVF, a number comes back flagged as low, and suddenly it feels as though a clock has started ticking.

So let's slow down and look at what AMH actually is, what it can tell you and, just as importantly, what it can't.

What is AMH?

AMH stands for anti-Müllerian hormone. It is made by the small follicles in your ovaries, the tiny fluid-filled sacs that each hold an immature egg. The more of these small follicles you have, the more AMH ends up in your blood.

That is why AMH is used as a marker of "ovarian reserve", a rough guide to how many eggs you have left. It is a useful measure, but it is an estimate of quantity. It tells us nothing about the quality of those eggs.

What is a normal AMH level?

There isn't one number that is normal for everyone. AMH is usually highest in your twenties and falls steadily from there, so a result that is typical at 42 would look low at 28.

Labs also use different tests and different units. In the UK, results are usually given in pmol/L, while many websites and apps use ng/mL (to turn ng/mL into pmol/L, multiply by roughly 7). That is one reason the charts you find online rarely match your report. The fairest comparison is the reference range printed on your own result, read alongside your age.

What does a low AMH actually mean?

A low AMH means you probably have fewer eggs in reserve than average for your age. In some situations that is genuinely useful to know, but it is often stretched to mean things it doesn't.

What low AMH does not mean

• It doesn't mean you can't get pregnant naturally. In a well-known US study of 750 women aged 30 to 44 who were trying to conceive, those with low AMH were just as likely to get pregnant over a year as those with normal levels. You only need one egg each month, and a lower reserve doesn't stop you ovulating.
• It doesn't measure egg quality. Quality is mainly linked to age, which is why a 32-year-old with low AMH is in a very different position from a 42-year-old with the same result.
• It can't predict exactly when your menopause will happen, at least not precisely enough to plan your life around.

Where it does matter

• If you are planning IVF or egg freezing. AMH helps predict how many eggs are likely to be collected in one cycle, which helps a clinic choose the right medication dose and set realistic expectations. There is more on this on our Fertility & Me page.
• If you are thinking about timing. A low result can be a prompt to think about your plans sooner rather than later. It is information, not a countdown.
• Alongside other changes. A very low AMH together with periods that have become irregular or stopped before the age of 40 can point to premature ovarian insufficiency, which needs proper assessment.

Does low AMH cause symptoms?

No. Low AMH on its own doesn't cause any symptoms. If you have noticed changes such as irregular periods, hot flushes or night sweats, those are worth discussing with a doctor in their own right, whatever your AMH says.

What causes low AMH?

The biggest factor by far is age. Other things that can be linked to a lower reserve include previous surgery on the ovaries, endometriosis affecting the ovaries, chemotherapy or radiotherapy, smoking and some genetic conditions. Often, though, there is no particular cause. A lower reserve is simply how some of us are made.

It is also worth knowing that the reading itself can come back lower for reasons that have nothing to do with your eggs. Hormonal contraception can temporarily lower AMH, and results vary between tests and labs. In a large Australian study, around a third of women who were retested after a low result had a normal result the second time.

Can you increase your AMH?

Not in any meaningful way. You will find plenty of supplements, diets and treatments that claim to raise AMH, but there is no good evidence that any of them improve your chances of having a baby. Looking after your general health is always worthwhile, and stopping smoking genuinely matters, but please be wary of anyone selling you a fix for a number.

Should you have an AMH test at all?

It depends on what you want to know. If you are about to start IVF or are seriously considering egg freezing, it is a helpful test. If you are simply curious about your fertility and not trying for a baby yet, it is worth knowing that, on its own, AMH can't tell you how likely you are to get pregnant. A low result can cause a lot of worry without giving you anything useful to act on.

What to do if your AMH is low

• Look at your result alongside your age, not in isolation.
• If you have been trying to conceive for a year without success, speak to your GP about fertility investigations. If you are 36 or over, don't wait a full year.
• If your periods have become irregular or stopped, see your GP, whatever your AMH result.
• If you are considering IVF or egg freezing, ask the clinic how your AMH changes their plan, which dose they would recommend and what they realistically expect.

Being handed a number without anyone explaining what it means for you is one of the most common reasons people come to us. We will look at your result alongside your history, talk you through what it means and help you work out your options, with nothing to sell you. If that would help, get in touch.

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