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

Abstract

Cesarean delivery rates remain high and variable across hospitals, regions, and countries. 1,2 Cesarean delivery may be a risk factor for childhood obesity, 1,2 possibly because delivery route can influence the intestinal microbiomes, 3 which may influence energy regulation. Two meta-analyses, summarizing data from 24 studies, have reported an increased risk of obesity for individuals with cesarean birth (pooled odds ratio [OR], 1.22 [95% CI, 1.05-1.42] and 1.33 [1.19-1.48]). 1,2 Limitations of earlier studies include small sample size in several studies and lack of adjustment for maternal body mass index (BMI [calculated as weight in kilograms divided by height in meters squared]) and sociocultural factors. Even after adjusting for these measured maternal characteristics, residual confounding is likely. Within-family analysis is one way of controlling for such confounding. Because siblings grow up in similar social, economic, and cultural environments and share the same genetic predisposition to obesity, sibling studies minimize the variation in several of the noncausal factors that could explain why cesarean delivery could appear to be associated with a higher risk of obesity. The main objective of this study was to examine within-family and additional between-family associations of delivery route with BMI z score at 5 years of age in a large cohort of sibling pairs to separate most putative confounding effects from the effects of cesarean delivery.

The Impact of Caesarean Section on the Risk of Childhood Overweight and Obesity: New Evidence from a Contemporary Cohort Study

“…Inability to account for elective and emergency CS calls into question the findings and conclusions of a sibling-control study 23 which suggested a causal link between CS birth and future obesity. Another study with a sibling-control design, albeit also limited by inability to distinguish between elective and emergency CS, did not find an association between CS birth and higher BMI z score at age five years 56 . Unfortunately, the GUI cohort did not have data that allows sibling-cohort analysis.…”

Association between caesarean section delivery and obesity in childhood: a longitudinal cohort study in Ireland

“…The declining influence of CS birth on the risk of obesity as children grow older has been attributed to the increasing influence of other risk factors for obesity like physical inactivity, family dietary habits, watching television (and the use of other electronic devices) 42. Indeed, a study which utilised a sibling-pair design attributed the observed association between CS birth and childhood obesity to unmeasured confounding 43…”

Caesarean delivery is associated with higher risk of overweight in the offspring: within-family analysis in the SUN cohort

“…Though the association between CD and high risk of overweight/obesity has been previously reported, our study presents some important novel information: within-family analyses have rarely been used to study this association and, as a result of different approaches, findings have been contradictory in previous assessments. 25 26 Within-family analyses help to minimise the effect of unmeasured family environmental and genetic factors, but we acknowledge that these analyses could also add confounding by nonshared confounders, as previously reported. 22 Although our results in within-family analyses may represent the upper bound of the real association between CD and offspring’s risk of overweight/obesity, these findings reinforce the idea that the observed association would be hardly explained only by residual confounding.…”

“…In the absence of randomised trials, the best possible evidence regarding the association between CD and offspring’s overweight comes from observational studies with appropriate design and careful analyses. The three main strategies used to minimise residual confounding 12 are (1) multivariable adjustment for shared risk factors for CD and childhood overweight, (2) subgroup analyses differentiating elective versus nonelective CD or procedures performed before or after the onset of labour and (3) within-family analyses 25 26 that compare the weight status of siblings discordant on the mode of delivery. In this study, we used these three strategies and also quantified the effect of unmeasurable confounding using the E-value.…”