Ovarian Reserve
Definition
Ovarian reserve is the remaining quantity and quality of a woman's eggs at any given point in her reproductive life. It declines steadily from birth and accelerates after age 35, ultimately reaching the threshold at which the ovaries can no longer sustain regular ovulation — the biological basis of menopause.
In Depth
A female is born with her entire lifetime supply of oocytes — roughly one to two million at birth, declining to about 300,000-400,000 at puberty through a process called atresia. From puberty onward, only a few hundred eggs will ever ovulate; the rest are lost steadily, with the rate accelerating after age 35 and again sharply in the late 30s and early 40s. When the remaining reserve falls below approximately 1,000 follicles, regular cyclic function can no longer be maintained, and the menopause transition begins.
Ovarian reserve is measured clinically with three main tools: anti-Müllerian hormone (AMH), a blood test reflecting the size of the remaining follicle pool; antral follicle count (AFC), an ultrasound count of small visible follicles; and FSH, which rises as reserve falls. AMH is the most stable and most commonly used marker.
It is important to distinguish ovarian reserve from fertility. A low AMH predicts a shorter remaining reproductive window and weaker response to fertility treatment, but does not by itself predict the chance of natural conception in any given month. Equally, ovarian reserve testing is not a reliable predictor of the exact age at menopause — it provides a rough trajectory, not a date.
Why It Matters
Ovarian reserve testing is increasingly used in midlife to anticipate the transition, evaluate fertility, and counsel women considering pregnancy in their late 30s or 40s. Understanding its limits prevents over-interpretation of a single AMH value.