CONCEPTIONS What is the ‘‘ovarian reserve’’? When I use a word, Humpty Dumpty said in rather a scornful tone, it means just what I choose it to mean—neither more nor less. Lewis Carroll The terms ovarian reserve and ovarian aging or senescence, often linked with diminished or premature are widely used in the scientific literature, in information aimed at consumers considering assisted reproduction or delaying pregnancy and sometimes by the media. Rarely are these terminologies clearly defined, and it is likely that they mean different things to different people. This lack of clarity muddies the waters for researchers and clinicians and can potentially mislead practitioners and patients in their understanding of ovarian aging and of therapies on their fertility and fecundity. There is a need to define carefully what is meant by these terms and restrict their usage appropriately, or alternatively to abandon them in favor of more clearly defined and transparent expressions. We propose using the term ovulatory potential to indicate the size of the growing follicle pool, which supports normal follicle progression and ovulation and can potentially be recruited to maturity (e.g., in assisted conception). The size of the growing follicle pool (ovulatory potential) only indirectly (and variably) reflects the size of the nongrowing primordial follicle population, the arbiter of the female reproductive lifespan, which is the true ovarian reserve.

WHAT ASPECTS OF THE OVARIAN FOLLICLE POOL CAN BE MEASURED? Antral follicle count (AFC) and serum markers are frequently used to assess the ovarian reserve and detect ovarian aging. The AFC, assessed by ultrasound, measures the number of antral follicles >2 mm in diameter. Preantral follicles and those