Secular trends in age at menarche among women born between 1955 and 1985 in Southeastern China

BACKGROUND Improvements in socioeconomic conditions and population health have been linked to declining age at menarche. In China, secular trends in age at menarche following extensive economic reform during recent decades have not been thoroughly investigated. This study examined the overall trend in age at menarche and assessed differences in the rate of change of age at menarche over time, and between urban and rural populations and education levels in southeastern China. METHODS Age at menarche was retrospectively collected from 1,167,119 Han Chinese women born 1955-1985, who registered in the Perinatal Health Care Surveillance System in 19 cities and counties in two southeast provinces during 1993-2005. Multivariable linear regression was used to estimate trends in age at menarche overall and stratified by urban/rural residence and education level. RESULTS Age at menarche declined by 0.33 [95% CI 0.33, 0.32] years/decade overall, with the fastest decline in women born in 1966-1975. For the earliest birth cohorts (1955-1965), age at menarche declined faster in urban versus rural regions, and for women with high school education or above versus primary school or less. In contrast, age at menarche declined slower among urban women born 1976-1985, and among those with higher education born 1966-1985. CONCLUSIONS Mean age at menarche declined for women born in 1955-1985 in southeast China. Further study is warranted to identify specific factors contributing to earlier age at menarche and associated health outcomes.