title: Secular trends in age at menarche among women born between 1955 and 1985 in Southeastern China.
abstract: 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.
authors.affiliation: Department of Child Health Development, Capital Institute of Pediatrics, Beijing, China. lvyanyu2008@gmail.com.|School of Public Health, Peking University Health Science Center, Beijing, China. lvyanyu2008@gmail.com.|Maternal-Infant Care Research Centre, Mount Sinai Hospital, Toronto, Ontario, Canada. lvyanyu2008@gmail.com.
authors.forename: Yanyu
authors.initials: Y
authors.lastname: Lyu
authors.affiliation: Maternal-Infant Care Research Centre, Mount Sinai Hospital, Toronto, Ontario, Canada. LMirea@mtsinai.on.ca.|Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada. LMirea@mtsinai.on.ca.
authors.forename: Lucia
authors.initials: L
authors.lastname: Mirea
authors.affiliation: Maternal-Infant Care Research Centre, Mount Sinai Hospital, Toronto, Ontario, Canada. JYang@mtsinai.on.ca.
authors.forename: Junmin
authors.initials: J
authors.lastname: Yang
authors.affiliation: Maternal-Infant Care Research Centre, Mount Sinai Hospital, Toronto, Ontario, Canada. RWarre@mtsinai.on.ca.
authors.forename: Ruth
authors.initials: R
authors.lastname: Warre
authors.affiliation: MOE-Shanghai Key Laboratory of Children's Environmental Health, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China. junjimzhang@gmail.com.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Maternal-Infant Care Research Centre, Mount Sinai Hospital, Toronto, Ontario, Canada. sklee@mtsinai.on.ca.|Department of Paediatrics, University of Toronto, Toronto, Ontario, Canada. sklee@mtsinai.on.ca.
authors.forename: Shoo K
authors.initials: SK
authors.lastname: Lee
authors.affiliation: School of Public Health, Peking University Health Science Center, Beijing, China. lulichee66@gmail.com.
authors.forename: Zhu
authors.initials: Z
authors.lastname: Li
mesh_terms: D000293:Adolescent; D017677:Age Distribution; D002681:China; D015988:Cohort Effect; D004522:Educational Status; D005260:Female; D006304:Health Status; D006801:Humans; D008572:Menarche; D012189:Retrospective Studies; D012424:Rural Population / Q000639:trends*; D014505:Urban Population / Q000639:trends*