title: Early Life Factors and Inter-Country Heterogeneity in BMI Growth Trajectories of European Children: The IDEFICS Study.
abstract: BACKGROUND
  Starting from birth, this explorative study aimed to investigate between-country differences in body mass index (BMI) trajectories and whether early life factors explain these differences.
  
  
  METHODS
  The sample included 7,644 children from seven European countries (Belgium, Cyprus, Germany, Hungary, Italy, Spain, Sweden) participating in the multi-centre IDEFICS study. Information on early life factors and in total 53,409 repeated measurements of height and weight from 0 to <12 years of age were collected during the baseline (2007/2008) and follow-up examination (2009/2010) supplemented by records of routine child health visits. Country-specific BMI growth curves were estimated using fractional polynomial mixed effects models. Several covariates focussing on early life factors were added to the models to investigate their role in the between-countries differences.
  
  
  RESULTS
  Large between-country differences were observed with Italian children showing significantly higher mean BMI values at all ages ≥ 3 years compared to the other countries. For instance, at age 11 years mean BMI values in Italian boys and girls were 22.3 [21.9;22.8; 99% confidence interval] and 22.0 [21.5;22.4], respectively, compared to a range of 18.4 [18.1;18.8] to 20.3 [19.8;20.7] in boys and 18.2 [17.8;18.6] to 20.3 [19.8;20.7] in girls in the other countries. After adjustment for early life factors, differences between country-specific BMI curves became smaller. Maternal BMI was the factor being most strongly associated with BMI growth (p<0.01 in all countries) with associations increasing during childhood. Gestational weight gain (GWG) was weakly associated with BMI at birth in all countries. In some countries, positive associations between BMI growth and children not being breastfed, mothers' smoking during pregnancy and low educational level of parents were found.
  
  
  CONCLUSIONS
  Early life factors seem to explain only some of the inter-country variation in growth. Maternal BMI showed the strongest association with children's BMI growth.
authors.affiliation: Leibniz Institute for Prevention Research and Epidemiology - BIPS, Bremen, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Börnhorst
authors.affiliation: Unit of Epidemiology and Population Genetics, Institute of Food Sciences, National Research Council, Avellino, Italy.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Siani
authors.affiliation: Unit of Epidemiology and Population Genetics, Institute of Food Sciences, National Research Council, Avellino, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Russo
authors.affiliation: Research and Education Institute of Child Health, Strovolos, Cyprus.
authors.forename: Yannis
authors.initials: Y
authors.lastname: Kourides
authors.affiliation: Department of Public Health, Ghent University, Ghent, Belgium.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Sion
authors.affiliation: Department of Pediatrics, University of Pécs, Pécs, Hungary.
authors.forename: Denés
authors.initials: D
authors.lastname: Molnár
authors.affiliation: GENUD (Growth, Exercise, Nutrition and Development) Research Group, Faculty of Health Sciences, University of Zaragoza, Zaragoza, Spain.
authors.forename: Luis A
authors.initials: LA
authors.lastname: Moreno
authors.affiliation: GENUD (Growth, Exercise, Nutrition and Development) Research Group, Faculty of Health Sciences, University of Zaragoza, Zaragoza, Spain.|IIS Aragón (Aragon Health Research Institute), Zaragoza, Spain.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Rodríguez
authors.affiliation: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
authors.forename: Yoav
authors.initials: Y
authors.lastname: Ben-Shlomo
authors.affiliation: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.|MRC Integrative Epidemiology Unit at the University of Bristol, Bristol, United Kingdom.
authors.forename: Laura
authors.initials: L
authors.lastname: Howe
authors.affiliation: Section for Epidemiology and Social Medicine, Department of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Lauren
authors.initials: L
authors.lastname: Lissner
authors.affiliation: Section for Epidemiology and Social Medicine, Department of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Mehlig
authors.affiliation: Section for Epidemiology and Social Medicine, Department of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.|School of Health and Welfare, Halmstad University, Halmstad, Sweden.
authors.forename: Susann
authors.initials: S
authors.lastname: Regber
authors.affiliation: Institute for Public Health and Nursing Research (IPP), Faculty for Human and Health Sciences, University Bremen, Bremen, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Bammann
authors.affiliation: Leibniz Institute for Prevention Research and Epidemiology - BIPS, Bremen, Germany.
authors.forename: Ronja
authors.initials: R
authors.lastname: Foraita
authors.affiliation: Leibniz Institute for Prevention Research and Epidemiology - BIPS, Bremen, Germany.|Faculty of Mathematics and Computer Science, University of Bremen, Bremen, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Ahrens
authors.affiliation: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
authors.forename: Kate
authors.initials: K
authors.lastname: Tilling
mesh_terms: D000367:Age Factors; D015992:Body Mass Index; D002648:Child; D002657:Child Development; D002675:Child, Preschool; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009765:Obesity / Q000453:epidemiology; D011247:Pregnancy; D012307:Risk Factors; D044465:White People