Defining menopausal status in epidemiologic studies: A comparison of multiple approaches and their effects on breast cancer rates.

OBJECTIVES: Menopausal status is a common covariate in epidemiologic studies. Still, there are no standard definitions for menopausal status using observational data. This study assesses distinctions between menopausal status definitions using commonly collected epidemiologic data, and explores their impact on study outcomes using breast cancer rates as an example. STUDY
DESIGN: Using survey data from 227,700 women aged 40-64 who received screening mammograms from the Breast Cancer Surveillance Consortium, we classified menopausal status under five different definitions: one complex definition combining multiple variables, two definitions using age as a proxy for menopausal status, one based only on menstrual period status, and one based on age and menstrual period status. MAIN OUTCOME MEASURES: We compared the distribution of menopausal status and menopausal status-specific breast cancer incidence and detection rates across definitions for menopausal status.
RESULTS: Overall, 36% and 29% of women were consistently classified as postmenopausal and premenopausal, respectively, across all definitions. Menopausal status-specific breast cancer incidence and detection rates were similar across definitions. Rates were unchanged when information regarding natural menopause, bilateral oophorectomy, hormone therapy, and timing of last menstrual period were sequentially added to definitions of postmenopausal status.
CONCLUSIONS: Distinctions in menopausal status definitions contribute to notable differences in how women are classified, but translate to only slight differences in menopausal status-specific breast cancer rates. Copyright 2010 Elsevier Ireland Ltd. All rights reserved.