title: Caesarean section and adiposity at 6, 18 and 30 years of age: results from three Pelotas (Brazil) birth cohorts.
abstract: Association between caesarian section (C-section) and obesity is controversial and mostly based on body mass index (BMI), which has inherent limitations. Using direct estimates of body fat mass, we aimed to assess the association between C-section and adiposity using fat mass index and BMI z-score in three birth cohort studies from Pelotas, Brazil.
  
  
  
  We measured weight, height and fat mass (using dual X-ray absorptiometry (DXA)) at ages 6, 18 and 30 years among participants in the 2004, 1993 and 1982 population-based Pelotas Birth Cohort Studies, respectively. We used multiple linear regression analysis to examine the crude and adjusted association between C-section and the body composition indicators. We also modelled height as an outcome to explore the presence of residual confounding.
  
  
  
  We observed that fat mass index and BMI z-score were strongly and positively associated with C-section in the crude analysis. However, when we adjusted for socioeconomic characteristics, maternal BMI, parity, age and smoking during pregnancy, effect estimates were attenuated towards the null, except for 30-year-old women. In those women from the 1982 cohort, C-section remained associated with fat mass index (β = 0.82; CI95% 0.32;1.32) and BMI z-score (β = 0.15; CI95% 0.03;0.28), even after adjusting for all potential confounders, suggesting an increase in fat mass index and BMI at 30 years among those born by C-section.
  
  
  
  We found no consistent association of C-section with fat mass index measured by DXA and BMI z-score in individuals aged 6, 18 and 30 years, except for women in the latter group, which might be explained by residual confounding. Confounding by socioeconomic and maternal characteristics accounted for all the other associations.
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil. abarros.epi@gmail.com.
authors.forename: Aluisio J D
authors.initials: AJ
authors.lastname: Barros
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil.|Federal University of Pampa, Itaqui, Brazil.
authors.forename: Leonardo Pozza
authors.initials: LP
authors.lastname: Santos
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil.
authors.forename: Fernando
authors.initials: F
authors.lastname: Wehrmeister
authors.affiliation: Post-graduate Program in Health and Behaviour, Catholic University of Pelotas, Itaqui, Brazil.
authors.forename: Janaina Vieira Dos Santos
authors.initials: JV
authors.lastname: Motta
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil.|Department of Preventive Medicine, School of Medicine, University of São Paulo, São Paulo, Brazil.
authors.forename: Alicia
authors.initials: A
authors.lastname: Matijasevich
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil.
authors.forename: Ina S
authors.initials: IS
authors.lastname: Santos
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil.
authors.forename: Ana M B
authors.initials: AM
authors.lastname: Menezes
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil.
authors.forename: Helen
authors.initials: H
authors.lastname: Gonçalves
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil.
authors.forename: Maria Cecília Formoso
authors.initials: MC
authors.lastname: Assunção
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil.
authors.forename: Bernardo L
authors.initials: BL
authors.lastname: Horta
authors.affiliation: Post-graduate Program in Epidemiology, Federal University of Pelotas, Rua Marechal Deodoro, 1160 - 3o piso, 96020-220, Pelotas, Brazil.|Post-graduate Program in Health and Behaviour, Catholic University of Pelotas, Itaqui, Brazil.
authors.forename: Fernando C
authors.initials: FC
authors.lastname: Barros
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue; D050154:Adiposity; D000293:Adolescent; D000328:Adult; D001823:Body Composition; D015992:Body Mass Index; D001835:Body Weight; D001938:Brazil; D002585:Cesarean Section; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000209:etiology*; D011247:Pregnancy
keywords: Adiposity; Body composition; Cesarean section; Cohort studies