Anti-Müllerian Hormone (AMH) is a protein produced by the granulosa cells surrounding the small, developing follicles within the ovaries. This hormone regulates the early growth and selection of these follicles, which contain immature eggs. Measuring AMH concentration in the blood provides a valuable estimate of a woman’s ovarian reserve—the remaining quantity of eggs and the functional capacity of the ovaries. Since AMH levels remain relatively stable throughout the menstrual cycle, they serve as a consistent marker for assessing reproductive potential and predicting the ovarian response to fertility treatments.
The Primary Influence: Biological Age
Age is the most significant factor determining a woman’s AMH level. AMH directly correlates with the pool of primordial follicles, which are fixed at birth and decrease continuously over a lifetime. This natural decline means AMH levels follow a predictable, downward trajectory throughout the reproductive years.
AMH levels are typically highest in early adulthood, peaking around age 25, before beginning a steady descent. The rate of decline accelerates noticeably as a woman moves into her late thirties. For instance, the median AMH value often falls below 1.2 ng/mL around age 36, indicating a diminished ovarian reserve for many women.
This accelerated drop reflects the rapid depletion of the remaining follicle pool as a woman approaches menopause. The average yearly decrease in AMH can be approximately 0.2 ng/mL/year through the mid-thirties. While age provides the baseline expectation for AMH, individual variation remains substantial. Therefore, a woman’s AMH level is a better indicator of her personal ovarian reserve than her chronological age alone.
Specific Health Conditions Affecting Ovarian Reserve
Certain chronic medical conditions can alter AMH levels, resulting in readings that are unusually high or low for a woman’s age. Polycystic Ovary Syndrome (PCOS) is associated with elevated AMH. In PCOS, the ovaries contain a large number of small, arrested follicles that accumulate.
Because AMH is secreted by the granulosa cells of these follicles, their sheer number causes an overexpression of the hormone. Women with PCOS commonly exhibit AMH levels two to four times higher than age-matched women without the condition. This high reading reflects an abundance of small follicles and is often used as a diagnostic criterion for PCOS.
Conversely, conditions like Premature Ovarian Insufficiency (POI) and severe Endometriosis are associated with low AMH levels. POI involves the loss of normal ovarian function before age 40, leading to a profound reduction in the follicle pool.
Endometriosis, particularly when it forms ovarian cysts known as endometriomas, may also hasten the decline of AMH. The inflammatory environment created by endometriomas can damage surrounding ovarian tissue, causing accelerated loss of follicles. Women with endometriosis often present with lower baseline AMH levels, suggesting the disease process compromises the ovarian reserve.
Impact of External Medical Interventions
External medical factors can significantly influence AMH measurements, causing temporary suppression or permanent damage. Hormonal contraceptives temporarily suppress AMH production. Medications like oral contraceptive pills introduce exogenous hormones that inhibit the natural ovarian cycle.
This suppression reduces the growth and activity of the small follicles that produce AMH. Women using hormonal contraceptives may have AMH levels 25 to 30% lower than non-users. This effect is temporary and typically reverses within a few months after stopping the medication, allowing AMH levels to return to baseline.
In contrast, certain medical treatments cause irreversible damage to the ovarian reserve. Chemotherapy and radiation therapy used to treat cancer are gonadotoxic, meaning they damage the ovaries. Chemotherapy often causes a rapid drop in AMH levels, which may become undetectable shortly after treatment begins.
The extent of this permanent damage depends on the woman’s age and the specific drugs used. Additionally, ovarian surgery, especially for the removal of cysts, can inadvertently damage healthy ovarian tissue containing follicles. For example, the surgical removal of endometriomas is linked to a post-operative reduction in AMH due to the unavoidable excision of functional ovarian cortex.
Lifestyle and Environmental Factors
While age and health conditions are the primary drivers, certain lifestyle factors can contribute to accelerated AMH decline. Smoking is the factor most consistently associated with a negative impact on ovarian reserve. Active smokers, especially in the late reproductive years, have AMH levels approximately 44% lower than non-smokers.
The toxic components in cigarette smoke damage ovarian follicles, accelerating their depletion. Fluctuations in Body Mass Index (BMI) and nutritional status also have an effect, though the relationship is complex. Low levels of Vitamin D may correlate with lower AMH, possibly due to its role in AMH gene function. However, these lifestyle factors typically exert a less pronounced influence than age or disease.