What is AMH and how is it useful

When a girl is born she has thousands of undeveloped follicles (eggs) in the ovary. Obviously these don’t all go on to become mature and ovulated during her lifetime. The majority of them fizzle out and never become a mature egg.

Egg development goes through stages – 1. Primordial follicles (the undeveloped bank of eggs). 2. Antral follicles (half-developed eggs) and 3. Mature or dominant follicles. It is the  mature follicles that go on to be ovulated, normally one at a time.

The process of which eggs go on to be developed and ovulated  is controlled by a hormone called anti-mullerian hormone (nicknamed AMH). AMH is both produced by the antral follicles and limits their maturation. This is a regulatory system common in endocrinology called “negative feedback”. The diagram below is helpful

Eventually the follicle stimulating hormone (FSH) secreted by the pituitary gland takes over and encourages one antral follicle to go on to become a mature egg.

So, what is the usefulness of the AMH test? It has been called the “egg counter” because it is a measure of the egg store in the ovary. Really, it is a measure of eggs at antral follicle stage. In teenagers it is very high and in women getting close to menopause it is very low or not detectable.

In PCOS the term “polycystic” really refers to “poly-antral” follicles, not cysts at all. Therefore the AMH, because it is produced by antral follicles is usually high in PCOS. Many people think that it could be a better marker of PCOS than the ultrasound. It really measures the same thing but in a different way and could be developed to be more accurate than ultrasound because we could have proper normal ranges for age. This is still being investigated.

The other usefulness of AMH is predicting safety of ovulation induction or IVF. If a woman has a very high AMH that means there are very many follicles sitting in the ovary at antral stage. The medication given to stimulate ovulation is FSH and can stimulate all of those half-developed follicles to mature at once. This is called super-ovulation or in extreme cases hyperstimulation.

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