Anti-Müllerian Hormone (AMH) is a protein hormone that reliably indicates a woman’s ovarian reserve, representing the remaining supply of eggs. The amount of AMH circulating in the blood reflects the size of the pool of follicles available to mature. The trajectory of AMH levels is not a simple straight line but rather a curve that changes speed across the reproductive lifespan. Understanding the specific rate of this reduction and the factors that accelerate it is important for informed family planning.
Understanding Anti-Müllerian Hormone (AMH)
AMH is produced by the granulosa cells that encircle the eggs within the ovaries. Specifically, it is secreted by small, growing follicles, known as preantral and small antral follicles, which are less than four millimeters in diameter. AMH plays a regulatory role by inhibiting the premature recruitment of resting follicles into the growth cycle, acting as a brake on follicular depletion. Unlike other reproductive hormones, AMH levels remain relatively stable throughout the menstrual cycle, making it a convenient measure of ovarian reserve via a simple blood test.
The Standard Trajectory of AMH Decline
The concentration of AMH follows a predictable, non-linear pattern of decrease across a woman’s reproductive years. Levels typically peak or plateau during the early twenties, reflecting the largest number of small, growing follicles. This peak is followed by a gradual, steady reduction that marks the initial phase of ovarian aging.
During the late twenties and early thirties, the decline is relatively slow, often progressing at an approximate rate of five to ten percent per year. For example, a woman at age 30 may have a median AMH level around 2.5 nanograms per milliliter (ng/mL). This phase of slow loss continues until a distinct point of acceleration is reached.
The steepest part of the decline typically begins in the mid-thirties, often around age 35 to 37. At this point, the rate of follicular loss accelerates significantly, sometimes increasing to 15 to 20 percent or more annually. This rapid drop means the median AMH value may fall to around 1.5 ng/mL by age 35 and continues downward sharply into the forties, becoming nearly undetectable near menopause.
Non-Age Factors Influencing AMH Levels
While chronological age is the primary determinant of AMH decline, several external and medical factors can cause AMH levels to drop more quickly. Certain medical interventions, such as chemotherapy or radiation, are known to be gonadotoxic, directly damaging the granulosa cells that produce AMH. For example, chemotherapy can cause AMH levels to plummet immediately, sometimes falling from a baseline of approximately 3.0 ng/mL to 0.3 ng/mL during treatment.
Surgical procedures involving the ovaries can also lead to a measurable, sudden decrease in AMH. The laparoscopic removal of endometriomas, cysts associated with endometriosis, is particularly noted for this effect. This surgery can cause an immediate drop in AMH levels, with studies showing a decline of 50 to 70 percent compared to pre-surgery baseline levels. The reduction is often more severe with bilateral surgery or when excessive cautery is used near the ovarian tissue.
Lifestyle choices, such as active smoking, are strongly associated with a faster rate of follicular depletion. Current smokers often exhibit significantly lower AMH values than non-smokers of the same age, with some research indicating a 44 percent lower AMH in late-reproductive age women who smoke. Additionally, genetic predisposition plays a role, as some women naturally begin life with a smaller primordial follicle pool, leading to lower AMH levels throughout their reproductive years.
Clinical Interpretation of AMH Measurement
In a clinical setting, AMH measurement is used primarily to estimate the remaining reproductive time horizon and predict the ovarian response to fertility treatments. For patients undergoing in vitro fertilization (IVF), AMH is a tool for predicting the number of eggs likely to be retrieved after ovarian stimulation. For instance, a serum AMH level below 1.0 to 1.26 ng/mL is often a threshold used to predict a poor ovarian response, suggesting a low yield of fewer than four oocytes.
Conversely, a high AMH level, often above 3.5 ng/mL, can predict a hyper-response to stimulation, helping clinicians manage the risk of Ovarian Hyperstimulation Syndrome (OHSS). Physicians use these specific numerical cut-offs to tailor medication dosage for each patient, optimizing the outcome while maintaining safety.
It is important to recognize that AMH only measures the quantity of the remaining egg supply. AMH is considered a poor predictor of egg quality, which is the genetic health of the eggs. Egg quality is overwhelmingly determined by chronological age, meaning a younger woman with a low AMH level still has a higher probability of producing genetically normal eggs than an older woman. Therefore, a low AMH alone does not predict infertility or the chance of natural conception in the short term.