The human body is born with a finite, non-renewable supply of eggs, collectively known as the ovarian reserve. This reserve represents the remaining quantity of reproductive cells available over a person’s lifetime. While counting the exact number of microscopic eggs is impossible without invasive procedures, medical science uses reliable, non-invasive methods to estimate this supply. Assessing the ovarian reserve provides valuable insight into reproductive health and helps predict the timeline for potential fertility. This assessment relies on measuring specific hormonal markers and physically counting early-stage egg follicles.
Measuring Ovarian Reserve with AMH
The primary and most informative blood test for estimating the quantity of the ovarian reserve measures the level of Anti-Müllerian Hormone, or AMH. This hormone is secreted by the granulosa cells surrounding the small, developing follicles within the ovaries. These early-stage follicles are a direct reflection of the remaining egg pool.
Because AMH is produced by these numerous small follicles, its concentration in the bloodstream provides a strong correlation with the size of the overall reserve. A significant advantage of the AMH blood test is that the hormone levels remain relatively stable across the entire menstrual cycle. This cycle-independence means the test can be performed on any day, offering a consistent snapshot of the egg supply. As the ovarian reserve naturally declines with age, the AMH level will gradually decrease, making it a valuable marker for the remaining reproductive lifespan.
The Role of FSH and Estradiol
Alongside AMH, Follicle-Stimulating Hormone (FSH) and Estradiol (E2) tests are frequently used to assess ovarian function. Unlike AMH, which measures quantity, FSH and Estradiol provide insight into how hard the ovaries are working to recruit and mature an egg. These blood tests are typically performed on the second or third day of the menstrual cycle, when hormone levels are at their baseline.
FSH is released by the pituitary gland to stimulate the growth of ovarian follicles. When the ovarian reserve is lower, the ovaries become less responsive, requiring the pituitary gland to release higher amounts of FSH. An elevated FSH level on Day 3 suggests the ovaries are struggling to respond, indicating a diminished reserve. Estradiol is measured concurrently because an abnormally high level can artificially suppress FSH, potentially masking a true decline in ovarian function.
Physical Assessment Through Ultrasound
A complementary, non-hormonal method for assessing the egg supply is the Antral Follicle Count (AFC), which uses a transvaginal ultrasound. Antral follicles are small, fluid-filled sacs, typically measuring between two and ten millimeters, that house immature eggs. The AFC involves a specialist visually counting all these small follicles present in both ovaries at the beginning of a menstrual cycle.
The total number of antral follicles counted provides a physical assessment of the egg pool available for that cycle. A higher count generally correlates with a greater ovarian reserve and a better response to ovarian stimulation medications. However, the AFC is considered highly operator-dependent, meaning the technician’s skill and experience can influence the result. Furthermore, the count can exhibit natural, physiological variation from one month to the next, unlike the relative stability of AMH.
Interpreting Test Results and Fertility Outlook
The numbers obtained from the AMH, FSH, and AFC tests are combined to create a comprehensive picture of the ovarian reserve. For instance, an AMH level below 1.0 nanograms per milliliter, or a Day 3 FSH level above 10 milli-international units per milliliter, often indicates a significantly diminished ovarian reserve. Similarly, a total AFC below five to seven is considered low. These results primarily serve as strong predictors of the number of eggs that might be retrieved during fertility treatments, such as in vitro fertilization.
It is important to understand that these markers measure egg quantity, not egg quality. Egg quality, defined by genetic health and the ability to form a viable embryo, remains the most significant factor for achieving a pregnancy. Quality is overwhelmingly determined by age, a factor not directly measured by these tests. Therefore, while a low ovarian reserve suggests a need to consider conception sooner, a person’s age provides the most reliable information regarding the predicted quality of the remaining eggs and the overall fertility outlook.