title: Socioeconomic disparities in birth weight and body mass index during infancy through age 7 years: a study within the Danish National Birth Cohort.
abstract: Socioeconomic inequalities in birth weight and in body mass index (BMI) later in childhood are in opposite directions, which raises questions about when during childhood the change in direction happens. We examined how maternal and paternal education and household income were associated with birthweight z-scores and with BMI z-scores at age 5 and 12 months and 7 years, and we examined the socioeconomic differences in the tracking of these z-scores across infancy and childhood.
  
  
  
  The associations were studied in a cohort of children in the Danish National Birth Cohort, single born between 1997 and 2003, for whom information on body size from at least 1 of 4 time points (n=85 062) was recorded. We examined the associations using linear mixed-effects modelling.
  
  
  
  Children from families with a low maternal and paternal educational level changed their body size z-scores upwards between birth and age 7 years. At age 5 and 12 months, there were no educational gradient. A low maternal educational level was associated with lower birth weight for gestational age z-scores at birth for boys (-0.199; 95% CI -0.230 to -0.169) and girls (-0.198; 95% CI -0.229 to -0.167) and higher BMI z-scores at age 7 for boys (0.198; 95% CI 0.154 to 0.242) and girls (0.218; 95% CI 0.173 to 0.264). There was not a similarly clear pattern in the tracking between different household income groups. However, a low household income level was associated with higher z-scores of both birth weight and BMI at age 7 years, but with a much weaker gradient at 5 and 12 months.
  
  
  
  The educational gradient shifts from positive with birth weight, to none during infancy to inverse with BMI at age 7 years. In contrast, the income gradient was positive at birth and at 7 years and much weaker during infancy.
authors.affiliation: Department of Clinical Epidemiology (formerly Institute of Preventive Medicine), Copenhagen, Denmark.|Section of Social Medicine, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Camilla Schmidt
authors.initials: CS
authors.lastname: Morgen
authors.affiliation: Section of Biostatistics, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Per Kragh
authors.identifier: 0000-0002-4296-8488
authors.initials: PK
authors.lastname: Andersen
authors.affiliation: Section of Social Medicine, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Laust Hvas
authors.initials: LH
authors.lastname: Mortensen
authors.affiliation: MRC Integrative Epidemiology Unit, The University of Bristol, and School of Social and Community Medicine, University of Bristol, Bristol, UK.
authors.forename: Laura D
authors.initials: LD
authors.lastname: Howe
authors.forename: Mette
authors.initials: M
authors.lastname: Rasmussen
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors.forename: Pernille
authors.initials: P
authors.lastname: Due
authors.affiliation: Department of Clinical Epidemiology (formerly Institute of Preventive Medicine), Copenhagen, Denmark.|MRC Integrative Epidemiology Unit, The University of Bristol, and School of Social and Community Medicine, University of Bristol, Bristol, UK.|Faculty of Health and Medical Sciences, Novo Nordisk Foundation Center for Basic Metabolic Research and Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Thorkild I A
authors.initials: TI
authors.lastname: Sørensen
authors.affiliation: Section of Social Medicine, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Anne-Marie Nybo
authors.initials: AN
authors.lastname: Andersen
mesh_terms: D001724:Birth Weight; D015992:Body Mass Index; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003718:Denmark; D004522:Educational Status; D005191:Family Characteristics; D005260:Female; D054624:Health Status Disparities; D006801:Humans; D007223:Infant; D007236:Infant, Small for Gestational Age; D008297:Male; D009035:Mothers; D063766:Pediatric Obesity / Q000209:etiology*; D012737:Sex Factors
keywords: Child BMI; SOCIAL MEDICINE; cohort study; obesity