title: Caesarean section delivery and the risk of allergic disorders in childhood.
abstract: BACKGROUND
  The composition of the intestinal flora in young children, if unfavourable, may increase the susceptibility to allergic disorders. Beneficial intestinal microbes originate from the maternal vaginal tract and thus are more likely to be transferred during vaginal births than during Caesarean sections (C-sections).
  
  
  OBJECTIVE
  To determine whether children born by C-section have a different risk of allergic disorders compared with those delivered vaginally. We also tested the hypothesis that the risk of allergic disorders is highest for children born after 'repeat C-sections'.
  
  
  METHODS
  A retrospective cohort study of 8,953 children aged 3-10 years. Children diagnosed with allergic rhinoconjunctivitis (AR), asthma, atopic dermatitis (AD), or food allergies were identified from the Kaiser Permanente Northwest Region electronic records. The children's sex, birth weight, birth order, postnatal exposure to antibiotics as well as the mothers' age, ethnicity, education, marital status, smoking status during pregnancy, and use of asthma or hayfever medications were identified through the mothers' medical records or through the Oregon Birth Registry.
  
  
  RESULTS
  The risk of being diagnosed with AR was significantly higher in the children born by C-section than in those delivered vaginally: adjusted odds ratio (OR)=1.37%, 95% confidence interval (CI)=1.14-1.63. Delivery by C-section was also associated with the subsequent diagnosis of asthma (OR=1.24%, 95% CI=1.01-1.53); this association was gender specific, with a positive association restricted to girls (OR for asthma in girls: OR=1.53%, 95% CI=1.11-2.10; in boys: OR=1.08%, 95% CI=0.81-1.43). There was no significant association between mode of delivery and AD. If children born in a 'repeat C-section' were considered separately the risk of being diagnosed with AR increased further (OR=1.78%, 95% CI=1.34-2.37). The same increase was noted for asthma in girls (OR=1.83%, 95% CI=1.13-2.97) but not in boys.
  
  
  CONCLUSIONS
  Caesarean sections may be associated with an increased risk of developing AR in childhood.
authors.affiliation: Oregon Health & Science University, Portland OR, USA. renpoh@pol.net
authors.forename: H
authors.initials: H
authors.lastname: Renz-Polster
authors.forename: M R
authors.initials: MR
authors.lastname: David
authors.forename: A S
authors.initials: AS
authors.lastname: Buist
authors.forename: W M
authors.initials: WM
authors.lastname: Vollmer
authors.forename: E A
authors.initials: EA
authors.lastname: O'Connor
authors.forename: E A
authors.initials: EA
authors.lastname: Frazier
authors.forename: M A
authors.initials: MA
authors.lastname: Wall
mesh_terms: D000890:Anti-Infective Agents / Q000627:therapeutic use; D001249:Asthma / Q000208:ethnology / Q000276:immunology; D001722:Birth Order; D002585:Cesarean Section / Q000009:adverse effects*; D002648:Child; D002675:Child, Preschool; D003233:Conjunctivitis, Allergic / Q000208:ethnology / Q000276:immunology; D003876:Dermatitis, Atopic / Q000208:ethnology / Q000276:immunology; D005260:Female; D005512:Food Hypersensitivity / Q000208:ethnology / Q000276:immunology; D006801:Humans; D006967:Hypersensitivity / Q000208:ethnology / Q000276:immunology*; D008297:Male; D008423:Maternal Age; D011247:Pregnancy; D019141:Respiratory System Agents / Q000627:therapeutic use; D012189:Retrospective Studies; D012221:Rhinitis, Allergic, Perennial / Q000208:ethnology / Q000276:immunology; D012307:Risk Factors; D012737:Sex Factors
chemical_list: D000890:Anti-Infective Agents; D019141:Respiratory System Agents