Association between caesarean birth and childhood cancer: An age-lagged approach

Aim We assessed the association between caesarean birth and age-specific risks of childhood cancer. Methods We followed a cohort of 1 034 049 children between 2006 and 2020 in Quebec, Canada, from birth until age 14 years. The exposure was caesarean, operative vaginal, or spontaneous vaginal birth. The outcome included haematopoietic or solid tumours. We calculated hazard ratios (HR) and 95% confidence intervals (CI) for the association between mode of delivery and childhood cancer in age-lagged analyses, adjusted for potential confounders. Results A total of 249 415 (24.1%) children were born by caesarean and 97 411 (9.4%) by operative vaginal delivery. Compared with spontaneous vaginal birth, caesarean was associated with 1.16 times the risk of any cancer (95% CI 1.04-1.30), 1.12 times the risk of haematopoietic cancer (95% CI 0.92-1.36) and 1.21 times the risk of solid tumours (95% 1.06-1.39). Associations strengthened at 2 years of age and were greatest for lymphoma and sarcoma. Operative vaginal birth was not significantly associated with the risk of cancer. Conclusion Caesarean birth may be associated with selected childhood cancers, including lymphoma and sarcoma early in childhood. The underlying reasons for the associations require further investigation, including whether mucosal dysbiosis or labour hormone exposure explain the excess risk.