title: Age at menarche and racial comparisons in US girls.
abstract: BACKGROUND
  Concern regarding change in the onset of sexual maturation of US girls has increased the need for current information on age at menarche from a national sample. Previous reports have been sparse and interpretation has been limited because of the racial composition and ages of the samples.
  
  
  OBJECTIVE
  The objectives of this study were to estimate the distribution of age at menarche for all US girls and for non-Hispanic white, black, and Mexican American girls in the Third National Health and Nutrition Examination Survey and to test for racial differences.
  
  
  METHODS
  Menstrual status data were collected from 2510 girls aged 8.0 to 20.0 years. The Third National Health and Nutrition Examination Survey followed a complex, stratified, multistage probability cluster design. SUDAAN was used to calculate proportions of girls reaching menarche at an age. Ages at menarche were estimated by probit analysis at the ages at which 10%, 25%, 50%, 75%, and 90% of the girls attained menarche.
  
  
  RESULTS
  Less than 10% of US girls start to menstruate before 11 years, and 90% of all US girls are menstruating by 13.75 years of age, with a median age of 12.43 years. This age at menarche is not significantly different (0.34 years earlier) than that reported for US girls in 1973. Age at menarche for non-Hispanic black girls was significantly earlier than that of white girls at 10%, 25%, and 50% of those who had attained menarche, whereas Mexican American girls were only significantly earlier than the white girls at 25%.
  
  
  CONCLUSIONS
  Overall, US girls are not gaining reproductive potential earlier than in the past. The age at menarche of non-Hispanic black girls is significantly earlier than that of non-Hispanic white and Mexican American girls.
authors.affiliation: Lifespan Health Research Center, Department of Community Health, Wright State University, School of Medicine, Dayton, Ohio, USA. cameron.chumlea@wright.edu
authors.forename: William Cameron
authors.initials: WC
authors.lastname: Chumlea
authors.forename: Christine M
authors.initials: CM
authors.lastname: Schubert
authors.forename: Alex F
authors.initials: AF
authors.lastname: Roche
authors.forename: Howard E
authors.initials: HE
authors.lastname: Kulin
authors.forename: Peter A
authors.initials: PA
authors.lastname: Lee
authors.forename: John H
authors.initials: JH
authors.lastname: Himes
authors.forename: Shumei S
authors.initials: SS
authors.lastname: Sun
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D044383:Black People; D002648:Child; D005260:Female; D006801:Humans; D008572:Menarche / Q000208:ethnology* / Q000502:physiology*; D017058:Mexican Americans; D011159:Population Surveillance; D011629:Puberty, Precocious / Q000453:epidemiology / Q000208:ethnology; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology; D044465:White People; D001741:Black or African American