Anti-Müllerian Hormone (AMH) is a protein hormone produced by the granulosa cells within the small, growing ovarian follicles. These follicles are tiny sacs that house immature eggs. Measuring AMH concentration in the blood provides a valuable estimate of a woman’s ovarian reserve, which represents the remaining supply of eggs. AMH testing is commonly used by clinicians to gauge reproductive lifespan and potential responsiveness to fertility treatments.
The Stability of AMH Across the Cycle
AMH’s general stability is a primary advantage compared to other reproductive hormones like Follicle-Stimulating Hormone (FSH) or Estradiol. Unlike FSH, which fluctuates dramatically, AMH levels remain relatively consistent throughout the monthly cycle. This stability is directly related to the hormone’s specific source within the ovary.
AMH is secreted by the preantral and small antral follicles, which are early stages of follicular development, measuring less than 10 millimeters in diameter. This pool of small follicles is not acutely sensitive to the rapid hormonal signals that govern the monthly selection of a single dominant follicle. Consequently, the collective output of AMH does not rise and fall sharply with the menstrual cycle phases.
This biological mechanism is what makes AMH a convenient and reliable marker for assessing ovarian reserve. Because the concentration is largely independent of the cycle, testing can be performed on any day of the month without requiring specific timing relative to menstruation or ovulation. While some studies have detected minor intra-cycle variations, these changes are generally not considered clinically significant enough to invalidate a single measurement.
What AMH Levels Indicate
The numerical result of an AMH blood test offers insight into the overall number of resting and growing follicles, but it does not measure egg quality. A typical normal range often falls between 1.0 ng/mL and 3.0 ng/mL. Interpretation must always be done in the context of a woman’s age, but results in this range generally suggest a healthy ovarian reserve.
A low AMH level, often below 1.0 ng/mL, suggests a diminished ovarian reserve and a smaller remaining pool of follicles. This finding can signal an earlier onset of menopause or suggest that the ovaries may not respond robustly to medication used during in vitro fertilization (IVF). Conversely, an exceptionally high AMH level, sometimes exceeding 3.5 ng/mL, may suggest an abundance of small follicles.
High AMH levels are frequently observed in women with Polycystic Ovary Syndrome (PCOS), which is characterized by an excessive number of small, undeveloped follicles. For women undergoing fertility treatment, AMH levels predict the ovarian response to stimulation drugs, helping clinicians tailor medication dosages. Higher AMH predicts a greater yield of eggs during an IVF cycle, but also increases the risk of Ovarian Hyperstimulation Syndrome (OHSS).
Key Non-Cyclical Factors That Influence AMH Results
While the AMH level does not significantly fluctuate from one week to the next within a single cycle, the number can change over a period of months or years due to several non-cyclical factors. The most significant biological determinant is chronological age, which causes a steady, irreversible decline in AMH as the total number of follicles naturally depletes over a woman’s reproductive lifetime.
Hormonal contraception is another factor that can artificially suppress AMH levels, potentially misleading test interpretation. Combined oral contraceptive pills, for example, can lower AMH readings by approximately 20% to 30%. This suppression is thought to be due to the temporary halting of follicle development while the medication is taken. This temporary suppression does not indicate a true loss of ovarian reserve, and levels typically rebound several months after stopping the medication.
A third source of variability is the inherent difference between the various laboratory assays used to measure AMH, which can produce slightly different numerical results from the same sample. Individuals tracking AMH over time are advised to use the same laboratory for sequential testing to ensure consistency. Research also suggests a possible association between severe Vitamin D deficiency and lower AMH levels, though the biological mechanism is not fully understood.