Do AMH levels vary across normal menstrual cycles?

Anti-mullerian hormone (AMH) is a commonly used biomarker of ovarian reserve. AMH levels decrease with age and reach undetectable levels approximately 5 years before menopause. AMH levels are thought to have minimal within-menstrual cycle variation compared with inhibin-B or follicle stimulating hormone (FSH). Unlike FSH levels, which are drawn on cycle days 2, 3 or 4, AMH levels can be drawn on any day of the cycle. Is this really true?

Sowers et al. from the University of Michigan, Ann Arbor, Michigan have described AMH variations across normal menstrual cycles (Fertil Steril 2010;94:1482-6). They analyzed daily blood samples from 20 healthy women aged 30 to 40 years who had regular menses across one menstrual cycle. They also measured another hormone (inhibin-B) but those data are not included in this blog.

Here are the results of the study.

They divided AMH results into 4 quartiles based on total AMH secretion over the cycle (Area-Under-The Curve Or AUC). The average AMH levels in the four quartiles were 0.67, 1.71, 3.02 And 5.33 ng/mL.

They describe two distinct patterns In AMH profiles.

• The AMH profile in the lowest AMH AUC quartile (Quartile I) had minimal variation throughout the menstrual cycle. This pattern was consistent with the commonly held belief that there is minimal variation of AMH across the menstrual cycle and this suggests an “Aging Ovary” pattern or Diminished Ovarian Reserve in the lowest quartile.
• There was a contrasting ‘‘Younger Ovary’’ pattern embodied in the remaining three quartiles where women had higher AMH profiles. These profiles demonstrated significant follicular phase AMH variation.

Notably, the chronologic ages of women with the ‘‘Aging Ovary’’ pattern were not significantly different than the mean chronologic ages of those women characterized as being in the ‘‘Younger Ovarian’’ Groups, albeit all women studied were between 30 to 40 years.

The authors conclude that AMH varies across the menstrual cycle differently based on the relative ovarian age rather than chronologic age. The “Younger Ovary” pattern had higher average AMH, higher AMH AUC and a rise in AMH during the first half (follicular phase) of the menstrual cycle. In contrast an “Aging Ovary” pattern shows a low average AMH level, low AMH AUC, shorter menstrual cycle lengths, and minimal variation In AMH levels during the cycle, suggesting Diminished Ovarian Reserve.

So what does all this mean?

If the AMH level is below 1 ng/mL, then this is likely indicative of a constituently low level and decreased ovarian reserve, and this interpretation could be made independent of the day of collection across the menstrual cycle. In contrast, interpretation of higher AMH levels will be dependent upon the day in which the specimen is collected within the menstrual cycle.

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