Secular Trends of Age at Menarche from 1985 to 2010 among Chinese Urban and Rural Girls

We sought to determine whether average age at menarche (AAM) declined in Chinese girls during the past decades, and whether there were any differences of AAM among urban and rural girls in the mainland of China. The analysis of the study was based on Han schoolgirls aged 9 to 18 years in 22-30 provinces during 6 cycles (1985, 1991, 1995, 2000, 2005 and 2010) of Chinese National Survey on Students’ Constitution and Health. The average AAM overall was determined using probit analysis and compared between urban and rural areas. Correlation analyses and line regression models were used to explore the relationship of socioeconomic factors with AAM. In 1985-2010 the median AAM decreased rapidly at the speed of 3.9 months/decade for urban girls from 13.17 year (95% CI, 13.14-13.20) to 12.35 year (95% CI,11.65-13.01) and 5.95 months/decade for rural girls from 13.83 year (95% CI, 13.80-13.85) to 12.59 years (95% CI, 12.36-12.82). The urban-rural difference reduced continuously from 0.66 year in 1985 to 0.24 year in 2010. The average AAM in southeastern areas was lower than that in the northwest, both in urban girls and rural girls. Higher relative Gross Domestic Product per capita and residents’ consumption level was consistently associated with increased likelihood of having reached menarche; the strength of associations for rural girls was stronger than that for urban girls. Our findings suggested presence of an obvious downward trend of AAM in Chinese girls from 1985 to 2010, both in urban and rural areas. The urban and rural distribution, regional difference and socioeconomic factors should be considered when interpreting trends in age at menarche in China.