Endocrine assessment of relative reproductive age in normal eumenorrheic younger and older women across multiple cycles

OBJECTIVE: The aim of this study was to better characterize the ranges and intercycle variability for day 3 follicle-stimulating hormone, estradiol, and inhibin B levels in normal eumenorrheic women. STUDY DESIGN: Healthy eumenorrheic volunteers were recruited, of whom 27 women were 20 to 25 years old (peak reproductive age) and 36 women were 40 to 45 years old (study population). Blood samples were obtained on day 3 of two consecutive menstrual cycles. In some women, an additional blood sample on day 3 was obtained within 1 year. RESULTS: In normal women aged 20 to 25 years versus women aged 40 to 45 years, the day 3 follicle-stimulating hormone geometric mean is 5.6 IU/L (95% CI, 3.3-9.5 IU/L) versus 9.6 IU/L (95% CI, 3.8-23.8 IU/L), the day 3 estradiol geometric mean is 44.0 pg/mL (95% CI, 20.4-95.0 pg/mL) versus 52.4 pg/mL (95% CI, 22.4-122.8 pg/mL), and the day 3 inhibin B geometric mean is 100.4 pg/mL (95% CI, 51.7-195.0 pg/mL) versus 52.4 pg/mL (95% CI, 9.5-289.3 pg/mL). Furthermore, 22% of women in the older age group have a normal day 3 follicle-stimulating hormone and estradiol level in one cycle but an elevated value in a consecutive cycle (P = .008). CONCLUSION: In women of peak reproductive age, the upper limit of day 3 follicle-stimulating hormone and estradiol levels are 9.5 IU/L and 95.0 pg/mL, respectively, and the lower limit of day 3 inhibin B level is 51.7 pg/ mL. If the initial day 3 follicle-stimulating hormone and estradiol levels in an older woman are normal, then a second measurement in a subsequent cycle should be obtained before counseling this woman regarding her reproductive potential.