Cesarean delivery and overweight at 6 years of age: a prospective cohort analysis of the Japan Environment and Children's Study.

Cesarean delivery (CD) has been suggested as a potential risk factor for childhood overweight and obesity; however, evidence beyond early childhood remains inconsistent. We examined the association between CD and childhood overweight at age 6 years and explored early life body mass index patterns including adiposity rebound (AR), in a large Japanese birth cohort. We analyzed 64,281 singleton mother-child pairs from the Japan Environment and Children's Study. Overweight at age 6 years was defined according to the International Obesity Task Force criteria. Logistic regression models were used to estimate adjusted odds ratios (aORs). Changes in overweight status between ages 3 and 6 years were examined to distinguish incident overweight from persistent overweight, and AR timing was evaluated. CD accounted for 18.5% of the births. Overweight at age 6 years was more frequent among children born by CD than among those born by vaginal delivery (10.7% vs. 8.8%). After adjusting for the prespecified covariates, CD was associated with higher odds of overweight at age 6 years (aOR 1.09, 95% confidence interval 1.02-1.16). In sex-stratified analyses, CD was associated with incident overweight between ages 3 and 6 years among females but not among males; however, the interaction between delivery mode and sex was not statistically significant. CD was not significantly associated with earlier AR.Conclusion: In this large Japanese cohort, CD was modestly associated with childhood overweight at age 6 years.