Anti-Müllerian Hormone (AMH) is a protein hormone secreted by the small, developing follicles within the ovaries. This hormone serves as a measurable indicator of the remaining supply of follicles, commonly referred to as the ovarian reserve. The level of this circulating hormone gradually declines over time as the follicle pool diminishes. Measuring AMH provides clinicians with a tool to assess a woman’s reproductive aging timeline and predict the transition toward the final menstrual period.
How AMH Reflects Ovarian Reserve
AMH is exclusively produced by the granulosa cells that surround the oocytes within the preantral and small antral follicles. The concentration of AMH in the bloodstream is directly proportional to the number of these growing follicles present in the ovaries. This allows AMH to serve as a reliable, quantitative marker for the remaining follicle pool.
AMH also regulates the rate at which resting primordial follicles are recruited into the growth phase. By inhibiting the progression from the primordial to the primary follicle stage, AMH helps manage the pace of follicle depletion. As the ovarian reserve declines with age, fewer follicles produce AMH, leading to a steady decrease in the hormone’s serum concentration. This decline begins long before the physical signs of reproductive aging become apparent, making AMH a predictive tool for the end of the reproductive lifespan.
Defining AMH Thresholds for Reproductive Stages
The AMH level indicating the menopausal transition is a point on a declining continuum where the hormone becomes nearly undetectable. Standardized staging systems, such as the Stages of Reproductive Aging Workshop (STRAW), categorize the late reproductive transition based on endocrine changes, including a marked fall in AMH. In the late menopausal transition, which precedes the final menstrual period, the AMH level typically falls below 0.5 nanograms per milliliter (ng/mL).
When AMH levels drop below approximately 0.1 ng/mL, or become “undetectable” by standard laboratory assays, it signals that the woman has either entered the late menopausal transition or is already postmenopausal. For women in their 40s, an AMH level of 0.39 ng/mL has been associated with a high probability of entering menopause within a few years. These numeric values serve as general guidelines, and the precise level indicating the final stage of reproductive capacity can vary based on the specific assay used by the laboratory.
Factors Influencing AMH Test Results
The measured concentration of AMH can be affected by several factors, leading to variability in test results. Variability between different laboratory assays is significant, as different testing platforms and kits may yield different absolute numbers for the same sample. This means a woman’s result could vary if tested at two different facilities, even if her true biological level remains unchanged.
The use of hormonal contraceptives, particularly combined oral contraceptive pills, can temporarily suppress AMH levels. Women using these medications may have AMH concentrations that are temporarily lower, sometimes by more than 20 percent, though the levels typically rebound after stopping the medication. Furthermore, the way a blood sample is handled after collection can influence the result. These technical and pharmacological factors require careful consideration when interpreting a single AMH result.
The Clinical Definition of Menopause
Although AMH provides a prediction of the timeline, menopause itself is defined as a clinical event, not solely a laboratory value. The official diagnostic criterion is the permanent cessation of menstrual periods for 12 consecutive months, in the absence of other medical causes. This twelve-month period of amenorrhea confirms that the ovaries have ceased their primary function.
In the clinical setting, a healthcare provider uses AMH levels in conjunction with other hormonal markers and reported symptoms to assess reproductive aging. Follicle-Stimulating Hormone (FSH) levels rise dramatically during the late menopausal transition as the body attempts to stimulate the few remaining follicles. An FSH level consistently above 25 mIU/L, combined with the absence of a period, supports the diagnosis of late perimenopause or postmenopause.