Caesarean section may be associated with suspected motor developmental delay at 3 years of age in the Japan Environment and Children's Study.

The number of births by caesarean section (CS) is increasing worldwide. In line with this trend, there is growing interest in the neurodevelopmental outcome of children born by CS. This study examined the relationship between the mode of delivery and suspected neurodevelopmental delay in young children. A total of 53,716 mother-child pairs participating in the Japan Environment and Children's Study, a representative Japanese cohort study of children, were included in the analysis of the association between CS and suspected developmental delay, as assessed by the Ages and Stages Questionnaires, Third Edition, in 3-year-old children. Multivariate logistic regression analysis was performed to calculate adjusted odds ratios (aORs) with 95% confidence intervals (CIs). No significant overall relationship was found between mode of delivery and suspected developmental delay. In an analysis by sex, CS was associated with increased risk of suspected gross motor developmental delay (aOR 1.27, 95% CI 1.07-1.49) in boys and increased risk of suspected fine motor developmental delay (aOR 1.34, 95% CI 1.11-1.63) in girls. These results suggest that there may be a relationship between CS and suspected motor developmental delay at the age of 3 years.