AMH (Anti-Müllerian Hormone)

Your ovaries hold a stock of follicles laid down before you were born, and from then on it only gets smaller. Each month a small group of follicles steps forward from that stock. Most of them disappear again, and at most one takes an egg to maturity. It is precisely those small, newly started follicles whose granulosa cells release AMH.

The amount of AMH in your blood is therefore roughly proportional to the size of that group, and so to the stock it came from. That is why the AMH value tracks so closely with the antral follicle count a gynaecologist performs on ultrasound: both estimate the same thing, one in blood and the other in an image.

What AMH counts is a number. It says nothing about the quality of the eggs in that stock, and it is quality that is strongly tied to your age and that largely determines the chance of a healthy pregnancy. A reassuring figure is therefore not a guarantee, and a disappointing figure is not a verdict.

At this stage the small follicles that make AMH grow without any signal from the pituitary. As a result AMH barely moves with the cycle, whereas FSH and estradiol differ sharply from one cycle day to the next and belong around day 3. That property, rather than the result itself, is the most useful thing you can know about this test.

The result is usually reported in µg/l, a unit numerically identical to the ng/ml used in the international literature. If your laboratory works in pmol/l, multiply by roughly 7.1.

Finally, look closely at the reference range printed on your result, usually 1.00 to 13.00 µg/l. That range is not adjusted for age. "Within the reference range" therefore means something entirely different for a woman of 24 than for a woman of 41. For the first, the same result may be low for her age; for the second it is comfortably average. Without an age beside it, an AMH value simply cannot be read.

AMH is the number many decisions around trying to conceive get built on, which is exactly why it pays to be precise about what it is strong at and what it says nothing about.

Where AMH is strong: predicting how your ovaries respond to hormonal stimulation. Because the value tracks the number of follicles that can be recruited, a doctor uses your AMH value in IVF to estimate three things. How many eggs a stimulation cycle is likely to yield. Which starting dose of gonadotropins fits. And how large the risk is of an over-response with ovarian hyperstimulation syndrome. A low value makes a modest yield more likely; a high value calls for more cautious dosing. The same logic applies to egg freezing: AMH helps estimate how many freezing cycles are needed to arrive at a realistic number of stored eggs. That makes the choice concrete rather than intuitive, and it is why the test has such a fixed place in fertility care.

Where AMH is not strong: predicting whether and when you will conceive naturally. In a study of women without a known fertility problem who had only just started trying (Steiner et al., JAMA 2017), women with a low AMH had no meaningfully lower chance of conceiving within six to twelve cycles than women with a normal value. A low value alongside a regular cycle therefore does not mean a natural pregnancy is off the table. Treat AMH as a planning number, not as a countdown clock. It helps you choose when to act, not whether it will work.

At the other end of the spectrum sits polycystic ovary syndrome. There AMH is often raised, because many small follicles stay active at once. The 2023 international PCOS guideline permits a raised serum AMH in adult women to be used as an alternative to ultrasound for establishing polycystic ovarian morphology (PCOM). PCOM is one of the three Rotterdam criteria, alongside signs of hyperandrogenism and ovulatory dysfunction, and two of the three must be met. A raised AMH can therefore stand in for one criterion, but it does not make the diagnosis. That stays with the doctor, who also looks at your cycle and at androgens such as total testosterone and the binding protein SHBG. Two hard limits come with it: AMH is not recommended for this purpose within eight years of a first period, and there is no internationally fixed cut-off. Whatever threshold a laboratory uses (around 3.2 µg/l on some platforms, for instance) is assay-specific.

Which brings us to the assay. AMH tests are not standardised. The same tube of blood can produce two different numbers at two laboratories. Never compare your result with a friend's from another provider, and follow your own value over the years only within one and the same laboratory.

AMH requires no planning. It can be drawn on any cycle day, including during your period, and there is no need to fast. That is the practical difference from the cycle-bound hormones, for which you have to fit in an appointment around cycle day 3.

Testing is most useful at the moments when you want to decide something: when you are considering egg freezing, when you are postponing trying to conceive and want to know where your reserve stands, ahead of an IVF or IUI pathway, when your cycle has been irregular or absent for months, and before and after ovarian surgery. Removing an endometriosis cyst often takes healthy ovarian tissue with it, so AMH can fall afterwards. A measurement beforehand gives you a starting point. After chemotherapy, AMH is likewise used to follow whether ovarian function recovers.

If your cycle is irregular or your period stops, AMH never stands alone. In the same draw your doctor will nearly always also look at prolactin and TSH, because a raised prolactin or a thyroid running fast or slow can disturb the cycle in exactly the same way.

If you use combined hormonal contraception (the pill, the ring or the implant), mention it when your result is interpreted. It suppresses AMH by roughly a quarter on average, and most strongly in women whose values are already on the low side. Your result then underestimates your true reserve. The effect is reversible and usually disappears within a few months of stopping. Never, however, stop your contraception on your own initiative to have a blood value measured; discuss it with your doctor.

The table below sets out AMH values by age: the median and the middle half of women from a large age-stratified cohort. These figures serve only as orientation, not as a cut-off.

This table shows why the printed reference range misleads. By around age 36 the median has already dropped below the widely used 1.2 µg/l threshold for diminished ovarian reserve: half of all women that age sit below it, with nothing wrong. An AMH of 0.5 µg/l at 40 falls outside the printed range and is entirely ordinary for that age. Note the third column as well: the spread within each age band is wide, so two healthy women of the same age can sit far apart. The figures were measured with one specific assay, and your laboratory may use different absolute values. Always have your result placed alongside your age, your cycle and your plans by a doctor.