The number of antral follicles in normal women with proven fertility is the best reflection of reproductive age.

Background: The purpose of this study was to compare the predictive capacity of several markers of reproductive age in normal women.

Methods: Healthy female volunteers (n = 162) aged 25-46 years with proven, normal fertility and regular menstrual cycles were recruited. In this selected group, chronological age was assumed to approximate reproductive age and, therefore, was taken as the proxy-variable for reproductive age. The number of antral follicles with 2-10 mm diameter, total ovarian volume, total follicular volume, mean follicular volume, and volume of either the smallest or largest ovary were estimated by transvaginal sonography of the ovaries. Serum levels of early follicular FSH, estradiol and inhibin B, as well as the response of estradiol and inhibin B to exogenous GnRH agonist administration (GAST), were also evaluated.

Results: Regression analysis revealed that the antral follicle number showed the highest correlation with age (r = -0.68, P = 0.001), and explained 46% of its variance. All other variables, except inhibin B, were moderately correlated with age. Responses of estradiol and inhibin B to the GnRH agonist were moderately correlated with age, but highly correlated with the number of antral follicles.

Conclusions: It is concluded that the number of antral follicles has the closest association with chronological age in normal women with proven fertility. As stimulated estradiol and inhibin B clearly reflect the size of the antral follicle cohort, the GAST may be considered the second best single test to predict reproductive age.