Estimating age of menopause in mothers in the ALSPAC Study: A data note.

Earlier menopause is associated with increased risks of type 2 diabetes, osteoporosis, heart disease, depression, and mortality. Although menopause is typically defined as the absence of menstruation for 12 consecutive months, deriving age at natural menopause using repeated, prospective data can be challenging. In this data note, we describe our approach developed to assign age at natural menopause using longitudinal data from the Avon Longitudinal Study of Parents and Children (ALSPAC) Mothers cohort and highlight the complexities involved. Between 2008 and 2020, women were asked at up to eight timepoints about their menstrual history, including when they last had a menstrual period (LMP), reasons for period cessation if relevant, and contraception and hormone replacement therapy (HRT) use. Our approach used these repeated menstrual reports to assign the timing of the final menstrual period. Specifically, we combined three key variables - self-reported LMP and menstruation in the last 3 months and last 12 months - and accounted for factors affecting menstruation such as surgery, contraception, and HRT. Age at natural menopause was then derived using these repeated reports across timepoints. Of 5,949 women included in the analysis (mean 3.6 timepoints per participant), age at natural menopause was assigned for 2,422 women. The mean assigned age of menopause was 49.4 years (SD = 4.1, range: 30-63 years, median = 50 years). This data note introduces potential users of the ALSPAC data to our derived menopause variable and highlights key challenges when using longitudinal data to estimate menopause timing including irregular bleeding, missing data, and conflicting reports. Our aim is to support researchers wishing to use this derived variable in future studies of reproductive ageing.