Factors that influence entry into stages of the menopausal transition.

OBJECTIVE: The aim of this study was to estimate the probabilities and identify risk factors for entering the menopausal transition and moving into each subsequent transition stage.
METHODS: Estimations of probabilities of entry into each menopausal transition stage and predictors associated with each transition stage were conducted in a population-based cohort of midlife women.
RESULTS: The likelihood of entering the menopausal transition and moving into each subsequent stage was increased for each unit increase in follicle-stimulating hormone (FSH) (P < 0.001) and with each unit decrease in inhibin B (P < 0.001) in the adjusted multivariable model. The largest observed change in average FSH levels was the comparison of women in the late transition (stage 4), with an average of 24.78 mIU/mL, to those in the early transition (stage 3), with 10.38 mIU/mL. Women experiencing this amount of change in FSH had an odds of transitioning from stages 3 to 4 of 1.90 (95% CI, 1.86-1.95). Decreases in inhibin B resulted in odds ratios similar to the magnitude of changes in FSH. Current smoking increased the odds of transition into each stage by approximately 30% (odds ratio, 1.30; 95% CI, 1.28-1.32). Average estradiol levels did not change dramatically between stages. However, higher estradiol significantly increased the odds of entering the transition (P = 0.013). Age and race predicted transitions into some but not all stages. Body mass index, alcohol use, and age at menarche did not predict entrance into any stage of the menopausal transition after adjusting for other study variables.
CONCLUSIONS: These results show that increased FSH, decreased inhibin B, and smoking strongly predict entry into the earliest stages of the menopausal transition as defined by changes in bleeding patterns. African Americans entered the transition before white women, but race did not predict entry into late transition stages. Higher estradiol levels predict entry into the earliest transition stage but not subsequent stages.