Objective: Cigarette smoking is a risk factor for earlier menopause. Animal studies show that in-utero smoke exposure is toxic to developing ovaries. Our aim was to evaluate whether in-utero smoke exposed women reach menopause earlier compared with nonexposed women.
Methods: This is a cohort study within the Avon Longitudinal Study of Parents and Children. Participants included in this study were followed from 1991/1992 until 2010. Participant characteristics for the current analysis were obtained from obstetric records and from annual follow-up questionnaires. When not available, age at natural menopause was estimated by age at filling in the questionnaire minus 1 year. Cox proportional hazards modeling was used to estimate hazard ratios of menopause for in-utero exposed and nonexposed women.
Results: There were 695/2,852 postmenopausal women, of whom 466 had natural menopause, 117 had hormonal therapy, and 112 had surgical menopause. Age at natural menopause was 50.6 ± 3.7 years. Of all participants, 20.2% (577/2,852) were exposed to smoke in-utero. Participants who were in-utero exposed but were not smokers did not have higher hazards of menopause (adjusted hazard ratio [HR] 0.92, 95% CI 0.72-1.18), whereas participants who were ever smokers (current or previous) and were in-utero exposed (adjusted HR 1.41, 95% CI 1.01-1.95) or were ever smokers but not exposed (adjusted HR 1.24, 95% CI 1.00-1.53) did have higher hazards of earlier menopause.
Conclusions: In-utero smoke exposure was not associated with earlier menopause, but the effect of in-utero smoke exposure was modified by the smoking habits of the participants themselves increasing the risk for smokers who were in-utero exposed.