A secular trend in age at menarche in Sendai city and its surroundings

A secular trend in age at menarche was examined for 1,333 women living in Sendai city and its surroundings by applying the birth-year cohort analysis and the cross-sectional probit analysis. The trend toward younger menarcheal ages was consistently observed by both analyses, and it started off soon after the second World War. The speed was 0.11 year/year for the observation period of 1946 to 1966.