Context/Objective: To characterize rates of change in serum estradiol (E2) levels across the menopausal transition and into early postmenopause.

Setting/Participants: Michigan Bone Health and Metabolism Study cohort of 629 women with median age of 38 (IQR=7) at the 1992/3 baseline with annual assessment of E2 levels over the subsequent 15-year period.

Design/Main Outcome Measures: Describe patterns of acceleration/decceleration in _logE2 rates of change before and after the final menstrual period (FMP) using non-parametric and piecewise regression modeling.

Results: Between -10 to -2 years to the FMP, mean fitted serum estradiol population values were relatively stable. The 95% confidence bands around the slight increase inE2 rate of change five years prior to the FMP included the value of no change. The fitted population mean E2 value declined 67% from 64.5 (standard error (SE)=3.6) pg/ml to 21 (SE=1.2) pg/ml in the four years between -2<FMP<+2. A second significant mean E2 rate of change was identified from 6–8 years post FMP. Fitted population mean E2 values declined 18% from 18.1 (SE=1.3) pg/ml at FMP=6 to 14.8 (SE=1.3) pg/ml at FMP=8. In non-obese women, the mean E2 percent decline was 42% from FMP=6 to FMP=8, whereas in obese women, the mean E2 percent decline over this time was 31%.

Conclusions: Population mean serum E2 levels were sustained until approximately 2 years prior to the FMP. In the ensuing 4-year period, E2 levels declined 67%. A secondary E2 decline, commencing about 6 years after the FMP, was observed in non-obese but not obese women.