BACKGROUND AND PURPOSE:

• Previous meta-analyses suggested that cesarean section is associated with increased BMI in offspring
• Confounding is a concern, even when adjusting for BMI
• One approach is to use within-family sibling data to control for environmental factors and shared genetic background
• Rifas-Shiman et al. (JAMA Pediatrics, 2018) sought to determine whether there is an association between mode of delivery and BMI of offspring

METHODS:

• Retrospective cohort study
• Data derived from the Linked CENTURY (Collecting Electronic Nutrition Trajectory Data Using Records of Youth) study
• Model adjusted for
  • Maternal age | Parity| Race & ethnicity
  • Child’s age | Sex | Birth year
• Data analyzed to assess within-family component and between-family component
• Main exposure: Route of delivery
• Primary outcomes: Age-specific and sex-specific BMI z-score (also called standard deviation score) at 5 years of age
  • BMI z-scores are measures of relative weight adjusted for child age and sex
  • 0.0 would represent 50^th percentile BMI while 2.5 would be >99^th percentile

RESULTS:

• 16,140 siblings were included from 8070 mothers
  • 19.9% of children had cesarean delivery
  • Mean (SD) BMI z-score at 5 years of age was 0.48 (1.00)
• Mean BMI z-score was
  • 0.45 among siblings who both had vaginal delivery
  • 0.51 among siblings with 1 cesarean and 1 vaginal delivery
  • 0.63 among siblings who both had cesarean delivery
• In co-variate adjusted model, the within-family association of cesarean vs vaginal delivery was not significant
  • 0.04 higher BMI z-score at 5 years of age (95% CI, −0.04 to 0.11)
• The addition of the between-family assessment changed association to 0.13 (95% CI, 0.04 to 0.22)
• In a model adjusted for the same covariates, but without decomposing the within-family and between-family effects, children with cesarean delivery had 0.13 higher BMI z score (95% CI, 0.08 to 0.17)

CONCLUSION:

• The authors found that within families, cesarean section was not associated with increase in BMI z-score at 5 years of age
• The authors conclude that previous studies, which found association with obesity and increased weight was limited by confounding

Learn More – Primary Sources:

Association of Cesarean Delivery With Body Mass Index z Score at Age 5 Years

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