title: Impaired fetal growth decreases the risk of childhood atopic eczema: a Swedish twin study.
abstract: BACKGROUND
  Studies have found associations between birth weight and risk of atopic eczema or allergic rhinitis (AR), although this could be due to confounding.
  
  
  OBJECTIVE
  We sought to evaluate associations between fetal growth and the risk of atopic eczema or AR in childhood, controlling for gestational age (GA), shared (familial) environmental and genetic factors.
  
  
  METHODS
  Data on atopic eczema, AR, birth characteristics and confounders were collected from registers and telephone interviews with the parents of 9- and 12-year-old twins. Firstly, cohort analyses on all twins (eczema n=10 132 and AR n=10 896) were performed. Secondly, to control for genetic and shared environment, co-twin-control analyses were performed in twin pairs discordant for atopic eczema (n=480) and AR (n=332).
  
  
  RESULTS
  The rate of atopic eczema increased with birth weight, from 12.6% in twin children <2000 g to 17.3% in children >or=3500 g. The rate of AR varied between 7.8% and 8.8%. In the cohort analyses, the odds ratio (OR) for atopic eczema was 1.62 (95% CI: 1.27-2.06) for 500 g increase in birth weight and 1.00 (95% CI: 0.75-1.33) for AR. In co-twin-control analyses on atopic eczema, OR was 3.93 (95% CI: 1.55-9.98) for 500 g increase in birth weight, with no significant difference between monozygotic and dizygotic twins (P=0.84).
  
  
  CONCLUSIONS
  We found a positive association between fetal growth and childhood atopic eczema, but not AR, independent of GA, shared environmental and genetic factors. This indicates fetal growth affects the immune system, and supports further studies on early mechanisms.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska University Hospital Solna, Stockholm, Sweden.
authors.forename: C
authors.initials: C
authors.lastname: Lundholm
authors.forename: A K
authors.initials: AK
authors.lastname: Ortqvist
authors.forename: P
authors.initials: P
authors.lastname: Lichtenstein
authors.forename: S
authors.initials: S
authors.lastname: Cnattingius
authors.forename: C
authors.initials: C
authors.lastname: Almqvist
mesh_terms: D001724:Birth Weight; D002648:Child; D015331:Cohort Studies; D003876:Dermatitis, Atopic / Q000503:physiopathology*; D005260:Female; D047109:Fetal Development; D006801:Humans; D007407:Interviews as Topic; D008297:Male; D006255:Rhinitis, Allergic, Seasonal / Q000503:physiopathology; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013548:Sweden; D014427:Twins