Anti-Müllerian Hormone (AMH) is a substance produced by the granulosa cells within the small, developing follicles of the ovaries. This hormone level directly reflects the size of the remaining pool of growing follicles, making it a reliable marker for a woman’s Ovarian Reserve, or her remaining egg supply. The answer is nuanced, as AMH is largely stable in the short term, but it is subject to several types of fluctuation, which can range from minor measurement noise to significant biological shifts.
Understanding AMH Stability Across the Menstrual Cycle
AMH is generally considered stable and independent of the hormonal fluctuations that define the monthly cycle. Unlike Luteinizing Hormone (LH) or Follicle-Stimulating Hormone (FSH), AMH does not follow a predictable, dramatic pattern across the menstrual phases. This stability is due to the source of the hormone: it is secreted by the pre-antral and small antral follicles, which are not yet responsive to acute, cycle-specific hormonal signals. This cycle-independent nature is a major advantage of the AMH test, allowing it to be drawn on any day of the month without requiring specific timing. Although newer, sensitive assays detect minor fluctuations (11-15% difference between phases), this variation is usually too small to change the clinical interpretation of the result.
Minor Variables Affecting AMH Test Results
Some temporary factors can cause a reading to appear lower or higher without reflecting a true, permanent change in the actual ovarian reserve. One significant factor is the use of hormonal contraceptives, such as the combined oral contraceptive pill. These medications can temporarily suppress AMH production, often resulting in a reading that is 20% to 30% lower than the woman’s true baseline. This drop is reversible, and levels typically rebound to their actual baseline within a few months after the medication is stopped.
Another source of apparent fluctuation is technical in nature, involving Assay Variability. Different laboratory testing methods or kits used at various facilities lack a single international standard, meaning results from different labs or different assays can vary by up to 10% to 20%. This is a difference in measurement, not a true biological change, which can make comparing tests done years apart problematic. A complex and inconsistent link exists between severe Vitamin D deficiency and AMH levels. Acute, severe physical stress or illness can also sometimes temporarily affect reproductive hormone readings, though these shifts are usually minor and transient for AMH.
Major Biological Changes That Alter AMH Levels
The most significant and inevitable change in AMH levels is the gradual, age-related decline. As a woman ages, the pool of primordial follicles naturally shrinks, leading to a corresponding, predictable decrease in AMH concentration over the course of years. This slow, continuous drop is the primary biological fluctuation AMH tracks, reflecting the ongoing depletion of the ovarian reserve.
Certain medical conditions and interventions can cause a sudden, rapid, or sustained change in AMH levels. Women with Polycystic Ovary Syndrome (PCOS) often have AMH levels that are two to three times higher than women of the same age without the condition. This elevated reading is due to the excessive number of small, undeveloped follicles characteristic of PCOS, each contributing to the overall AMH production.
Conversely, direct damage to the ovaries can cause an acute, permanent drop in AMH. Ovarian surgery, such as procedures to remove endometriosis or cysts, may inadvertently damage or remove healthy ovarian tissue, resulting in a sudden and significant decrease in the measurable AMH level. Highly toxic treatments, such as certain types of chemotherapy or pelvic radiation, can also rapidly destroy a large portion of the follicular reserve. The magnitude of this drop and the potential for recovery depend heavily on the woman’s age and her AMH level before treatment began.
Interpreting AMH Results and Retesting
Because AMH levels are influenced by both long-term biological decline and short-term variables, interpretation requires careful context. AMH should not be viewed in isolation; it functions best when considered alongside other factors like the Antral Follicle Count (AFC) determined by ultrasound and FSH levels. AMH is a quantitative measure of the egg supply, but it offers little information about the quality of the eggs.
Retesting is often recommended following any intervention known to cause a temporary shift. For example, a repeat AMH test several months after discontinuing hormonal contraceptives will provide a more accurate baseline of the ovarian reserve. Similarly, retesting is warranted after ovarian surgery or completion of a chemotherapy regimen to assess the post-treatment reserve. If an initial result is unexpectedly low or high, a specialist may recommend a second test to rule out measurement noise or assay variability before making major treatment decisions.