Ovarian reserve is the finite supply of eggs established before birth that naturally declines over a lifetime. Measuring this reserve is central to understanding a woman’s fertility potential, especially for family planning or before starting fertility treatments like In Vitro Fertilization (IVF). While age remains the strongest predictor of egg quality and reproductive success, ovarian reserve testing provides a measurable estimate of the quantity of eggs remaining. This estimated count helps reproductive specialists tailor treatment plans and offer personalized guidance regarding a woman’s reproductive timeline.
Understanding the Concept of Ovarian Reserve
Ovarian reserve is the capacity of the ovary to provide egg cells capable of leading to a successful pregnancy. A woman is born with her entire supply of eggs, housed within primordial follicles, and no new eggs are created after birth. The initial pool peaks during fetal development, consisting of millions of potential oocytes, but rapidly decreases to about 300,000 to 400,000 follicles by puberty.
The natural decline occurs continuously through atresia, where follicles spontaneously degenerate. This constant loss is minimally related to monthly ovulation. The decline accelerates significantly once a woman reaches her late 30s.
Ovarian reserve tests primarily measure the quantity of eggs remaining. The quality of the eggs, which relates to their genetic health and ability to result in a viable pregnancy, is strongly correlated with the woman’s age. A high egg count does not guarantee high quality, nor does a low count rule out a successful pregnancy.
Measuring Reserve Through Blood Markers
Estimating ovarian reserve often involves blood tests measuring specific hormone levels. These markers indirectly reflect the activity of growing follicles and the remaining egg pool. The most reliable marker is Anti-Müllerian Hormone (AMH), produced by the granulosa cells of small, growing follicles.
AMH levels correlate well with the number of follicles present. AMH can be measured at any point during the menstrual cycle because its levels remain relatively stable. A higher AMH level suggests a larger ovarian reserve, while a low level indicates a diminished reserve compared to the age group average.
Other important blood markers are Follicle-Stimulating Hormone (FSH) and Estradiol (E2), measured early in the menstrual cycle (typically day two, three, or five). FSH is the pituitary hormone that signals the ovaries to recruit and mature a follicle. High FSH levels (often above 10 IU/L) suggest the ovaries are not responding adequately, forcing the body to produce more FSH.
Estradiol is measured alongside FSH because elevated levels early in the cycle can suppress FSH production. A high basal Estradiol level can lead to an inaccurately low FSH result, masking a true decline in ovarian function. Testing these hormones together provides a more accurate picture of the communication between the brain and the ovaries.
Imaging Techniques for Egg Supply Estimation
The Antral Follicle Count (AFC) is a non-hormonal, imaging-based technique used alongside blood tests to estimate ovarian reserve. The AFC uses a transvaginal ultrasound to visualize and count the small fluid-filled sacs (antral follicles) within both ovaries. These follicles are typically 2 to 10 millimeters in diameter and represent the cohort of eggs recruited for potential maturation in that cycle.
The AFC is ideally performed during the early follicular phase (generally between day two and day five) when these small follicles are most visible. The total count from both ovaries provides a physical, real-time snapshot of the functional ovarian reserve. A normal total AFC often ranges from 9 to 21 follicles, though this varies by age.
A lower AFC, such as a count below 8 or 9, suggests a diminished ovarian reserve and a smaller pool of eggs available for recruitment. Since the AFC directly counts the structures that produce AMH, this measurement often correlates strongly with the AMH blood test result. Specialists frequently use both the AFC and AMH for a comprehensive assessment.
What the Results Reveal About Fertility
Ovarian reserve tests primarily predict ovarian responsiveness to fertility treatments, rather than the chance of natural conception. For women undergoing IVF, a high reserve (high AMH, high AFC, low FSH) suggests a better likelihood of retrieving a large number of eggs. Conversely, a low reserve indicates a diminished response to stimulation medications, meaning fewer eggs are likely to be retrieved.
A low egg count does not equate to an inability to conceive naturally. While low reserve can make conception more challenging, these tests measure quantity, and the ultimate success of pregnancy depends on quality.
For younger women, a low egg count is less concerning for natural fertility because the remaining eggs are statistically more likely to be genetically normal. Age remains the single most accurate predictor of egg quality and live birth rates. All results should be interpreted in the context of a woman’s age and clinical history, requiring consultation with a reproductive endocrinologist.