title: The association of preterm birth with severe asthma and atopic dermatitis: a national cohort study.
abstract: BACKGROUND
  Asthma and atopic dermatitis are both regarded as atopic diseases. Being born too early is associated with increased risk of asthma, but some studies have indicated that the opposite might be true for atopic dermatitis. We explored in more detail the associations between preterm birth, asthma, and atopic dermatitis.
  
  
  METHODS
  We analyzed data from Norwegian registries with prospectively collected data. All live births in Norway from 1967 through 2001 were followed through 2005 by linking the Medical Birth Registry of Norway to the National Insurance Scheme and to Statistics Norway. Only severe asthma and atopic dermatitis were registered in the National Insurance Scheme.
  
  
  RESULTS
  Of a total of 1,760,821 children, we identified 9,349 cases (0.5%) with severe asthma and 6,930 cases (0.4%) with severe atopic dermatitis. Compared with children born at term (37-41 wk gestation), preterm birth was associated with increased odds for severe asthma (odds ratio (OR) 1.7 (95% confidence interval (CI): 1.6-1.8) for 32-36 wk gestation and OR 3.6 (95% CI: 3.1-4.2) for 23-31 wk) and decreased odds for severe atopic dermatitis (OR 0.9 (95% CI: 0.8-1.0) for 32-36 wk gestation and OR 0.7 (95% CI: 0.5-1.0) for 23-31 wk). Adjustment for perinatal and socio-demographic factors weakened the association between gestational age and severe asthma, while slightly strengthening the association between gestational age and severe atopic dermatitis.
  
  
  CONCLUSIONS
  Preterm birth was associated with increased risk of severe asthma and decreased risk of severe atopic dermatitis.
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway; Department of Pediatrics, Haukeland University Hospital, Bergen, Norway.
authors.forename: Håvard
authors.initials: H
authors.lastname: Trønnes
authors.forename: Allen J
authors.initials: AJ
authors.lastname: Wilcox
authors.forename: Rolv Terje
authors.initials: RT
authors.lastname: Lie
authors.forename: Trond
authors.initials: T
authors.lastname: Markestad
authors.forename: Dag
authors.initials: D
authors.lastname: Moster
mesh_terms: D000293:Adolescent; D000328:Adult; D001249:Asthma / Q000453:epidemiology*; D015331:Cohort Studies; D003876:Dermatitis, Atopic / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D009664:Norway; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D015995:Prevalence; D012307:Risk Factors; D012959:Socioeconomic Factors; D055815:Young Adult
keywords: asthma; atopic dermatitis; gestational age; pregnancy complications; premature birth