title: Childhood asthma hospitalization risk after cesarean delivery in former term and premature infants.
abstract: BACKGROUND
  Cesarean delivery modifies infant gut bacterial flora composition, which may result in hindered tolerance to allergenic substances, thereby increasing the risk of asthma in accordance with the hygiene hypothesis. Results of previous studies regarding an association between birth route and asthma are conflicting, and these studies have not evaluated some potential confounding effects, including prematurity and maternal asthma.
  
  
  OBJECTIVE
  To determine whether cesarean delivery in full-term and premature infants increases the risk of subsequent childhood asthma hospitalization.
  
  
  METHODS
  We conducted a case-control study using the Washington State Birth Events Record Database linked to statewide hospitalization data. The study included 2,028 children hospitalized for asthma (cases) and 8,292 age-matched controls.
  
  
  RESULTS
  Cesarean delivery was modestly associated with an increased risk of asthma hospitalization (odds ratio [OR], 1.20; 95% confidence interval [CI], 1.04-1.39). However, when analyzed separately, there was an association between cesarean delivery and asthma hospitalization in premature infants (OR, 1.90; 95% CI, 1.09-3.02) but not in full-term infants (OR, 1.15; 95% CI, 0.97-1.34).
  
  
  CONCLUSIONS
  Cesarean delivery was associated with subsequent asthma hospitalization only in premature infants. Because mothers with asthma are reported to have increased rates of cesarean delivery and premature delivery, other factors in addition to the hygiene hypothesis, including genetic and in utero influences associated with maternal asthma, may contribute to the increased risk of asthma in premature infants.
authors.affiliation: Division of Pulmonary Medicine, University of Washington, Seattle, Washington, USA. jason.debley@seattlechildrens.org
authors.forename: Jason S
authors.initials: JS
authors.lastname: Debley
authors.forename: Jodi M
authors.initials: JM
authors.lastname: Smith
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Redding
authors.forename: Cathy W
authors.initials: CW
authors.lastname: Critchlow
mesh_terms: D000328:Adult; D001249:Asthma / Q000453:epidemiology* / Q000209:etiology*; D016022:Case-Control Studies; D002585:Cesarean Section / Q000009:adverse effects*; D002648:Child; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007234:Infant, Premature; D008875:Middle Aged; D011247:Pregnancy; D047928:Premature Birth / Q000150:complications*; D012189:Retrospective Studies; D012307:Risk Factors