title: Body mass index trajectories from ages 1 to 20: Results from two nationally representative canadian longitudinal cohorts.
abstract: OBJECTIVE
  In this study, unique body mass index (BMI) trajectories from ages 1 to 20 years were identified; each trajectory according to socio demographic and family characteristics was described.
  
  
  METHODS
  Participants came from two national population surveys (n = 7,253; n = 901) and were aged 1-6 years at baseline. Children were surveyed biennially over eight waves up to 14-20 years of age. BMI trajectories by sex and survey cohort were identified by group-based trajectory modeling. After crossvalidating trajectories between survey cohorts, the characteristics of trajectory membership were assessed by multinomial regression.
  
  
  RESULTS
  Four BMI trajectories were found: low, decreasing, medium, and high. The decreasing trajectory was characterized by an overweight or obese childhood followed by a normal-weight adolescence. The low, medium, and high trajectories were characterized by growth curves culminating, by age 20, to BMI 22.6, 29.3, and 34.9 kg/m(2) , respectively, for males and 20.6, 24.5, and 32.0 kg/m(2) , respectively, for females. Factors associated with the high trajectory included ethnicity and paternal education (female only), large for gestational age, rural area residence, and maternal smoking.
  
  
  CONCLUSIONS
  The identification and validation of four major trajectories reflect the heterogeneity in patterns of BMI development from 1 to 20 years.
authors.affiliation: School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Tu
authors.affiliation: School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Louise C
authors.initials: LC
authors.lastname: Mâsse
authors.affiliation: Faculty of Health Sciences, Simon Fraser University, Vancouver, British Columbia, Canada.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Lear
authors.affiliation: School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Carolyn C
authors.initials: CC
authors.lastname: Gotay
authors.affiliation: School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Chris G
authors.initials: CG
authors.lastname: Richardson
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D002170:Canada; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D009765:Obesity / Q000453:epidemiology*; D050177:Overweight / Q000453:epidemiology*; D011795:Surveys and Questionnaires; D055815:Young Adult