Anti-Müllerian Hormone (AMH) is a protein produced by specialized cells within the ovarian follicles, which are the fluid-filled sacs that contain eggs. This hormone serves as a reliable marker for assessing a woman’s ovarian reserve, representing the remaining pool of potential eggs available in the ovaries. Measuring AMH levels provides insight into the quantity of the egg supply, which is a significant factor in reproductive planning and the likelihood of success with fertility treatments. Because AMH levels generally reflect the number of small, growing follicles, this blood test has become a standard tool in evaluating reproductive potential.
The Role and Origin of Anti-Müllerian Hormone
AMH is a member of the transforming growth factor beta family, regulating the initial stages of follicle development. The hormone is exclusively produced by the granulosa cells that surround the developing egg inside the follicle. Specifically, AMH is secreted by small, actively growing follicles (pre-antral and small antral follicles) before they become dependent on Follicle-Stimulating Hormone (FSH) for further growth.
The level of AMH in the bloodstream provides an accurate estimate of the overall ovarian reserve. As a woman ages, the number of primordial follicles naturally decreases, leading to a corresponding decline in AMH levels. AMH is considered a superior indicator compared to other hormones, such as FSH, because its levels remain relatively stable throughout the menstrual cycle. This stability means the blood test can be performed at any time. The hormone also acts as an inhibitor, conserving the egg supply over time by preventing the premature recruitment of the primordial follicle pool.
Interpreting AMH Test Results
The AMH test provides a numerical value, usually measured in nanograms per milliliter (ng/mL), that reflects the egg quantity or functional ovarian reserve. This result must always be interpreted in the context of a woman’s age. A level considered normal for a woman in her 40s would be considered low for a woman in her 20s. A range of 1.5 ng/mL to 4.0 ng/mL is generally viewed as normal or optimal, while levels below 1.0 ng/mL may indicate a low ovarian reserve.
A severely low AMH level, often defined as less than 0.5 ng/mL, suggests a significantly reduced egg supply. As a woman ages, the average AMH level naturally declines. For instance, the average level for a 30-year-old might be around 2.5 ng/mL, dropping to approximately 1.5 ng/mL by age 35 and 1.0 ng/mL by age 40.
It is crucial to understand that AMH measures egg quantity and does not provide information about egg quality. Egg quality, which refers to the genetic health of the egg, is overwhelmingly determined by the woman’s age and is the most significant factor in the likelihood of a successful pregnancy. A younger woman with a low AMH may still have a healthy pregnancy if the remaining eggs are high quality. Conversely, an older woman with a high AMH level may have many eggs, but a higher proportion will be genetically abnormal, increasing the risk of miscarriage or failed implantation.
AMH and Assisted Reproductive Technologies
In the context of Assisted Reproductive Technologies (ART) like In Vitro Fertilization (IVF), AMH is a powerful tool used to predict how the ovaries will respond to stimulation medications. A strong positive correlation exists between a woman’s baseline AMH level and the number of eggs retrieved during an IVF cycle. Clinicians use this information to individualize the treatment protocol and determine the appropriate dosage of ovarian stimulation drugs.
A low AMH level predicts a “poor response,” suggesting fewer eggs will be retrieved, which prompts the physician to use a more tailored or higher-dose stimulation protocol. Conversely, a very high AMH level (often above 4.0 ng/mL) predicts a “hyper-response.” This carries an increased risk of Ovarian Hyperstimulation Syndrome (OHSS), a potentially serious complication. For these patients, the AMH result helps the medical team select a gentler stimulation protocol or lower medication doses to minimize the risk of OHSS.
Factors Influencing AMH Levels and Measurement
While AMH is a reliable marker, several external variables can influence its measured level or interpretation. The long-term use of hormonal birth control, such as oral contraceptive pills, can temporarily suppress AMH levels, leading to a reading up to 30% lower than the true underlying reserve. This suppression occurs because the exogenous hormones reduce the body’s own follicle-stimulating hormone (FSH), slowing the growth of the small AMH-producing follicles.
Conversely, conditions like Polycystic Ovary Syndrome (PCOS) typically cause AMH levels to be artificially inflated, often two to four times higher than in healthy women of the same age. This elevation is due to the increased number of small, undeveloped follicles characteristic of PCOS, with each follicle producing more AMH than normal.
Ovarian surgery, such as procedures to remove endometriosis cysts, can also directly damage the ovarian tissue and cause a significant, permanent drop in AMH levels. Furthermore, the specific laboratory assay used to measure the hormone can lead to slight variations in the reported result, which is why specialists always interpret a woman’s AMH level using the reference ranges provided by the testing laboratory.