title: Caesarean sections and risk of wheezing in childhood and adolescence: data from two birth cohort studies in Brazil.
abstract: BACKGROUND
  There is evidence from two meta-analyses that children born through caesarean section (C-section) may have an increased risk of developing asthma compared with those born through vaginal delivery. Objective To evaluate the association between mode of delivery and wheezing (current and persistent) in childhood and adolescence, in two birth cohort studies in Brazil.
  
  
  METHODS
  The outcome variable was based on the International Study of Allergy and Asthma questionnaire, which collects information about wheezing within the 12 months before the interview. Persistent wheezing was defined when it was present in more than one follow-up at different ages, in the 1993 cohort. The questions were asked to mothers when children were aged 4 years (1993 and 2004 cohorts) and directly to cohort participants at 11 and 15 years (1993 cohort). Mode of delivery was collected by the research team of each cohort when children were born.
  
  
  RESULTS
  Response rates in the last follow-up visit of the 1993 and 2004 cohorts were 85% and 92%, respectively. The prevalence of current wheezing increased from 20% to 28% at 4 years from 1993 to 2004; at 11 and 15 years, the prevalence was around 14% and 12%, in the 1993 cohort. The proportion of C-sections increased from 30.5% to 45% between 1993 and 2004. In each cohort, the prevalence of current wheezing was similar among children born through vaginal and C-section. The risk for persistent wheezing in the 1993 cohort was higher among girls born through C-section than boys.
  
  
  CONCLUSIONS
  Despite the increase in the proportion of C-section in two cohorts in Southern Brazil, we found no evidence of an association between mode of delivery and the subsequent risk of wheezing. Among girls, although there was no statistical significance, the risk was higher for those born by C-section, especially regarding persistent wheezing.
authors.affiliation: Postgraduate Programme in Epidemiology, Federal University of Pelotas, Pelotas, Brazil. anamene@terra.com.br
authors.forename: A M B
authors.initials: AM
authors.lastname: Menezes
authors.forename: P C
authors.initials: PC
authors.lastname: Hallal
authors.forename: A M
authors.initials: AM
authors.lastname: Matijasevich
authors.forename: A J D
authors.initials: AJ
authors.lastname: Barros
authors.forename: B L
authors.initials: BL
authors.lastname: Horta
authors.forename: C L P
authors.initials: CL
authors.lastname: Araujo
authors.forename: D P
authors.initials: DP
authors.lastname: Gigante
authors.forename: I S
authors.initials: IS
authors.lastname: Santos
authors.forename: G
authors.initials: G
authors.lastname: Minten
authors.forename: M R
authors.initials: MR
authors.lastname: Domingues
authors.forename: S C
authors.initials: SC
authors.lastname: Dumith
authors.forename: F C
authors.initials: FC
authors.lastname: Barros
mesh_terms: D000293:Adolescent; D001938:Brazil / Q000453:epidemiology; D002585:Cesarean Section / Q000009:adverse effects* / Q000706:statistics & numerical data; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007407:Interviews as Topic; D008297:Male; D012135:Respiratory Sounds / Q000209:etiology*; D012307:Risk Factors; D011795:Surveys and Questionnaires