We know female fertility (or fecundity, to be scientific about it) declines with age. There are two factors that play into this decline: quantity and quality. A woman is born with all the eggs she will ever have, and that number declines over the course of her life. The second reason that fertility declines with age is that the quality of a woman’s eggs also declines. As a woman gets older, fertilized eggs have a harder time separating their chromosomes correctly during cell division (remember meiosis from high school? That’s what we’re talking about here). When a fertilized egg doesn’t separate correctly, this can lead to miscarriage or chromosomal disorders, such as Down Syndrome.
There are ways to measure quantity of eggs, or ovarian reserve (an AMH blood test being one of the main ways) but there is not a good way to measure quality of eggs while they are in vivo (meaning, inside your body). However, a paper published this week in Fertility and Sterility provides some compelling data that AMH might be a marker of quality as well.
The study, first authored by Dr. Brianna Lyttle Schumacher of UNC, measured the AMH levels of women who were trying to get pregnant naturally and then had them take pregnancy tests every month and report back on whether or not they got pregnant, if they had a miscarriage and when they had a miscarriage. The authors found that, after adjusting for age, women with a clinical pregnancy loss (meaning after an ultrasound confirmed pregnancy but before 20 weeks) had the lowest AMH values. Specifically, if a woman’s AMH was less than or equal to 0.4 ng/mL (considered “significantly diminished ovarian reserve” by the authors), she had a 2.2 times higher risk of miscarriage than if her AMH was greater than 1 ng/mL. Interestingly, the authors also found that women with the highest AMH values were more likely to lose a pregnancy earlier, within four days of the first positive pregnancy test.
This study is interesting because the researchers were studying women with no known history of infertility, who were attempting to conceive naturally. Previous studies of the association of AMH and miscarriage have focused on women in infertility clinics doing IVF or women who have had recurrent miscarriages. The authors speculate that the association between low AMH and miscarriage might be particular to spontaneous, unexplained miscarriages.
The reason why AMH, a hormone produced by the cells that surround the eggs in your ovaries, could be a marker of egg quality remains unresolved. The authors decline to speculate as to the biological mechanism at work here that relates AMH levels to miscarriage. This study should also be interpreted in light of other studies that have on the whole demonstrated an equivocal relationship between AMH and time to pregnancy. One of those studies was first authored by Dr. Anne Steiner, who is also an author of the paper that is the subject of this summary. Hopefully more studies will explore what is going on at the cellular level so that we can finally have some insight into egg quality, as well as quantity, and get a better picture of female fecundity.