title: Cesarean section and risk of obesity in childhood, adolescence, and early adulthood: evidence from 3 Brazilian birth cohorts.
abstract: BACKGROUND
  The number of cesarean sections (CSs) is increasing in many countries, and there are concerns about their short- and long-term effects. A recent Brazilian study showed a 58% higher prevalence of obesity in young adults born by CS than in young adults born vaginally. Because CS-born individuals do not make contact at birth with maternal vaginal and intestinal bacteria, the authors proposed that this could lead to long-term changes in the gut microbiota that could contribute to obesity.
  
  
  OBJECTIVE
  We assessed whether CS births lead to increased obesity during childhood, adolescence, and early adulthood in 3 birth cohorts.
  
  
  METHODS
  We analyzed data from 3 birth-cohort studies started in 1982, 1993, and 2004 in Southern Brazil. Subjects were assessed at different ages until 23 y of age. Poisson regression was used to estimate prevalence ratios with adjustment for ≤15 socioeconomic, demographic, maternal, anthropometric, and behavioral covariates.
  
  
  RESULTS
  In the crude analyses, subjects born by CS had ∼50% higher prevalence of obesity at 4, 11, and 15 y of age but not at 23 y of age. After adjustment for covariates, prevalence ratios were markedly reduced and no longer significant for men or women. The only exception was an association for 4-y-old boys in the 1993 cohort, which was not observed in the other 2 cohorts or for girls.
  
  
  CONCLUSIONS
  In these 3 birth cohorts, CSs do not seem to lead to an important increased risk of obesity during childhood, adolescence, or early adulthood.
authors.affiliation: Postgraduate Program in Health and Behavior, Catholic University of Pelotas, Brazil. fcbarros.epi@gmail.com
authors.forename: Fernando C
authors.initials: FC
authors.lastname: Barros
authors.forename: Alicia
authors.initials: A
authors.lastname: Matijasevich
authors.forename: Pedro C
authors.initials: PC
authors.lastname: Hallal
authors.forename: Bernardo L
authors.initials: BL
authors.lastname: Horta
authors.forename: Aluísio J
authors.initials: AJ
authors.lastname: Barros
authors.forename: Ana B
authors.initials: AB
authors.lastname: Menezes
authors.forename: Iná S
authors.initials: IS
authors.lastname: Santos
authors.forename: Denise P
authors.initials: DP
authors.lastname: Gigante
authors.forename: Cesar G
authors.initials: CG
authors.lastname: Victora
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001938:Brazil / Q000453:epidemiology; D002585:Cesarean Section / Q000009:adverse effects*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000453:epidemiology / Q000209:etiology*; D015995:Prevalence; D012044:Regression Analysis; D012307:Risk Factors; D012737:Sex Factors; D055815:Young Adult