Timing and secular trend of pubertal development in Beijing girls

Background: Historical research is limited in changes in pubertal development in Chinese girls. We aimed to identify the timing of pubertal characteristics and the secular trend of menarche age among Beijing girls from the 1980s through the 2000s. Methods: Six data sets were analyzed, including the Beijing Child and Adolescent Metabolic Syndrome study in 2004, where 9778 Bejing girls aged 6-18 years were studied. The Fetal Origins of Adult Disease study provided retrospective menarche age from 1940 through 1960. Other four studies were conducted in Beijing to obtain supplementary information to assess secular trend in menarche age. Linear regression method was used to analyze the data. Results: Among Beijing girls in 2004, the median age at menarche was 12.1 years, which was 0.6 years earlier in urban than in rural areas. The median age at Breast Tanner Stage 2 was 9.5 +/- 1.2 years, representing 9.4 +/- 1.1 years and 9.6 +/- 1.2 years for urban and rural girls, respectively. In contrast, the median age at Pubic Hair Tanner Stage 2 was 11.1 +/- 1.1 years, representing 10.8 +/- 1.1 and 11.4 +/- 1.1 years for urban and rural girls, respectively. The menarche age of urban girls decreased by 4.2 months per decade, and that of rural girls by 9.6 months per decade from 1980 to 2004. Conclusions: Urban girls mature earlier than rural girls in Beijing. A secular trend towards earlier menarche was observed between the 1980s and the 2000s.