AGE AT NATURAL MENOPAUSE IN A POPULATION-BASED SCREENING COHORT - THEROLE OF MENARCHE, FECUNDITY, AND LIFE-STYLE FACTORS

Objective: To verify whether a population-based hypothesis (age at men arche and age at natural menopause have an inverse relationship) also applies at the level of the individual and to investigate what other f actors predict age at natural menopause. Design: Prospective cohort st udy (the Doorlopend Onderzoek Morbiditeit/Mortaliteit [DOM] project). Setting: Preventicon Breast Cancer Screening Centre, Utrecht, The Neth erlands.Patient(s): A cohort of 3,756 Dutch women, born between 1911 a nd 1925, participating in a population-based breast cancer screening p rogram, who experienced a natural menopause. Three samples of women we re studied: a sample who did not use oral contraceptives (OCs) (n = 3, 347), a sample of OC users (n = 409), and a combined sample of OC user s and nonusers (n = 3,756). Main Outcome Measure(s): Age at menopause and menarche, fertility patterns, OC use, height, weight, smoking, and demographic variables. Result(s): No relation was found between age a t menarche and age at natural menopause. The total percentage of varia nce in age at natural menopause explained by multiple regression inclu ding all factors was minimal, ranging from 1.3% to 9.7% in OC users. L inear regression analysis indicated a slight secular trend in age at m enopause. Conclusion(s): Frisch's hypothesis could not be corroborated at the individual level. These results suggest that age at menarche a nd menopause should be treated as independent risk factors for breast cancer. Modification of age at menopause by lifestyle factors (except possibly for OC use) appears minimal. Steril((R)) 1997;68:95-102. (C) 1997 by American Society for Reproductive Medicine.