title: [Geographic distribution and secular trend of menarche in 9-18 year-old Chinese Han girls].
abstract: OBJECTIVE
  To analyze the characteristics and secular trend of age at menarche (age at menarche, AAM) in Chinese girls aged 9-18.
  
  
  METHODS
  Probit analyses were used to calculate AAMs in various populations of Chinese girls who participated in National Physical Fitness and Health Surveillance in 2005 or 1995. The samples of girls were 92 767 in 2005 and 85 433 in 1995 National Physical Fitness and Health Surveillance, respectively.
  
  
  RESULTS
  AAM was 12.76 years in Chinese girls aged 9-18 in China. AAMs were 12.60 and 12.92 years for urban and rural girls, respectively. There was a large variation among different geographic areas, and AAM was earlier in girls living in east of China and later in girls living in northwest of China. AAMs of the top 5 municipalities/provinces were Beijing (12.27 years), Shanghai (12.32 years), Sichuan (12.48 years), Fujian (12.50 years) and Tianjin (12.51 years); and the last 5 provinces/autonomous regions were Qinghai (14.09 years), Hubei (13.33 years), Heilongjiang (13.10 years), Ningxia (13.08 years) and Hunan (12.87 years). AAMs were 0.22 and 0.34 years earlier than those of urban and rural girls in 1995.
  
  
  CONCLUSIONS
  The onset of menarche was generally earlier in urban than in rural girls, and the latest in northwest of China. Significant decline trend of age at menarche could be found in Chinese girls, especially in rural areas. The differences of AAMs among urban and rural areas and in various provinces were with a tendency to shrink in 2005 compared with 1995.
authors.affiliation: Institute of Child and Adolescent Health, Peking University School of Public Health, Beijing 100191, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Song
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
authors.forename: Pei-jin
authors.initials: PJ
authors.lastname: Hu
authors.forename: Bing
authors.initials: B
authors.lastname: Zhang
mesh_terms: D000293:Adolescent; D041923:Adolescent Development; D000367:Age Factors; D002648:Child; D002681:China / Q000453:epidemiology / Q000208:ethnology; D005260:Female; D006801:Humans; D008572:Menarche / Q000502:physiology*; D019371:Topography, Medical; D014505:Urban Population