title: Mode of delivery is associated with asthma and allergy occurrences in children.
abstract: OBJECTIVE
  A growing body of evidence indicates that perinatal factors modulate immune development and thereby may affect childhood asthma risk. In this study, we examined the associations between birth by cesarean section (C-section) and atopic disease occurrence in childhood.
  
  
  METHODS
  Subjects were born in California between 1975 and 1987 and were 8 to 17 years old during their enrollment in the Children's Health Study. Our analysis was restricted to 3464 children born at or after 37 weeks of gestation with a birth weight of 2500 g or greater based on birth certificate data. Information about sociodemographic factors, reported physician-diagnosed asthma, and other atopic diseases was obtained by using a self-administered structured questionnaire. Logistic regression models were fitted to compute odds ratios (ORs) and 95% confidence intervals (CIs).
  
  
  RESULTS
  Children born by C-section were at increased risk for asthma (OR, 1.33; 95% CI, 1.01-1.75), hay fever (OR, 1.57; 95% CI, 1.24-1.99), and allergy (OR, 1.26; 95% CI, 1.03-1.53) compared with those born vaginally. Risk associated with C-section was the same for children regardless of family history of asthma or allergy.
  
  
  CONCLUSIONS
  We conclude that birth by C-section or processes associated with it may increase the risk for atopic disease in childhood.
authors.affiliation: Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles 90033, USA.
authors.forename: Muhammad T
authors.initials: MT
authors.lastname: Salam
authors.forename: Helene G
authors.initials: HG
authors.lastname: Margolis
authors.forename: Rob
authors.initials: R
authors.lastname: McConnell
authors.forename: James A
authors.initials: JA
authors.lastname: McGregor
authors.forename: Edward L
authors.initials: EL
authors.lastname: Avol
authors.forename: Frank D
authors.initials: FD
authors.lastname: Gilliland
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000208:ethnology / Q000209:etiology*; D002585:Cesarean Section / Q000009:adverse effects*; D002648:Child; D005006:Ethnicity; D005260:Female; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000208:ethnology / Q000209:etiology*; D008297:Male; D012959:Socioeconomic Factors