Fun with Anti-Müllerian Hormone

So my post on CD3 reference ranges got me thinking... what is Anti-Müllerian Hormone, and why does it vary so much from woman to woman? Let's see what we can find out. (And by we, I mean me, and since I am definitely not a medical doctor I encourage you to do your own research on the matter.)

First of all, you kind of have to love Anti-Müllerian Hormone (AMH) for having an umlaut right in its name. And why does it have an umlaut? Because it inhibits the embryonic development of a structure named after a Dr. Müller: the Müllerian ducts. I know, usually when going through IVF we hear a lot about blasts and hatching and the really early stages of embryo development, but what happens after that is still pretty cool. Once in the womb, the embryo continues to develop structures that are common to all humans, like a gastrointestinal system (wouldn't want to be without that...), but very early on in the process - as in, during the first 8 weeks - the reproductive organs also begin to develop. And they develop in the same way for everybody at first, by creating the Müllerian ducts. If you're a girl, you want those ducts to stick around - they eventually turn into your uterus, Fallopian tubes, cervix, and most of your vagina. If you're a boy, however, you don't want those ducts to linger. You want Wolffian ducts instead, which eventually turn into the vas deferens, epididymis, and other structures that will someday allow you to (hey hey!) ejaculate. That's where AMH comes in. If the embryo is secreting AMH from the cells that will eventually turn into his testicles, then the Müllerian ducts die off. If there are no early-stage testicle cells creating AMH, those ducts just keep on keeping on, and the baby will be born with the kind of reproductive organs that someone will one day refer to as her downtown dining and entertainment district.

But, you say, I am not an embryo! Why is my doctor measuring the amount of AMH that I, an adult woman, am producing? If I were an embryo, I wouldn't be reading a blog about infertility, now would I? And I respond, because I can hear you all the way across the Internet, that there's more.

Adult women's ovaries also secrete AMH for their own personal use, and it controls the formation of follicles during the reproductive years. Ovulation is actually supremely cool: ovaries have lots of follicles in them that have the potential to become a mature egg, but how a lucky follicle is chosen to mature is not terribly well understood. (I kind of think of the follicles that do make it to ovulation like the Marines: the Few, the Proud. They grow to over a hundred times their original size and have to compete for the privilege of doing so.) AMH's role in this process appears to be as a kind of counterbalance to FSH, which stands for Follicle-Stimulating Hormone and which does pretty much what its name suggests. You need FSH to stimulate your follicles to grow so they can someday become a mature egg, but if you have too much of it, that can also be a problem - hence the role that AMH plays to limit the effectiveness of FSH. AMH is produced by follicles at very early stages of development, and if you take it away, the FSH does its job a little too well. Ideally, you want to strike a balance. More AMH = more early-stage follicles waiting patiently to develop. And less AMH = not as many follicles awaiting their turn to be used at a later date.

Now, AMH doesn't change during the menstrual cycle, unlike some hormones I could name (coughcough FSH and LH coughcough) but it does decline gradually over a woman's lifespan. Your ovaries age, their overall reserve declines, and there are fewer early-stage follicles hanging around to create this "we're waiting patiently" hormone. Most fertility literature relating to AMH focuses on what to do if your numbers are too low, since it's a common problem for women of a certain age seeking treatment. Although there's considerable disagreement on how low is too low for infertility treatment to be worthwhile, anything above 0.5 ng/mL is probably still good, and above 0.15 ng/mL is considered acceptable. Then again, if your AMH is too high, that can also lead to infertility. Your FSH may not be able to do its job at all - there might be too many follicles giving out the "we're waiting patiently!" signal for the FSH to be able to stimulate one to develop, and that can mean you're not ovulating.

But the thing is, like much in the world of infertility treatment, it's important not to look at just one lab value or test result. (Don't forget, there are lots of other hormones involved with this process - it's as complicated as it is fascinating.) And it's equally important to remember that many of these hormones can be messed with through medical intervention so your ovaries can do what they need to do. Women can, and do, conceive with AMH values that don't look perfect. They also conceive with missing Fallopian tubes, strangely-shaped uteri, and after drinking wayyyyy too many tequila sours. Talk to an RE if you want to know more about AMH, but whatever you do, don't mention that you read about this on a :::shudder::: blog. Blame Wikipedia for that. :-)