The association between caesarean section and childhood asthma: an updated systematic review and meta-analysis

Background: Investigating the association between caesarean section (SC) and childhood asthma has shown contradictory results in different studies. The present study was conducted to determine the association between SC and childhood asthma. Material and method: The present study was conducted based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. All the steps of the study were conducted independently by two reviewers from the inception until February 1, 2019. In case of disagreement, the third reviewer resolved it. We searched international online databases, including Scopus, Cochrane Library, PubMed/Medline, Embase, Web of Science (ISI), Science Direct, and Google scholar. The results of studies were combined using random effects model, and heterogeneity was measured through I-2 index and Cochran's Q test. Comprehensive Meta-Analysis Software was used for meta-analysis. The significance level of all tests was considered to be P < 0.05. Results: The heterogeneity rate was high (I-2 = 67.31%, P < 0.001) in 37 studies. The results showed that SC increased the risk of childhood asthma (RR (relative risk) = 1.20 [95% CI 1.15-1.25, P < 0.001]). The association between emergency and elective SC and childhood asthma was significant with RR of 1.18 (95% CI 1.07-1.29, P < 0.001) in 13 studies and 1.23 (95% CI 1.20-1.26, P < 0.001) in 13 studies, respectively. The subgroup analysis for RR of childhood asthma in SC indicated that study design (P = 0.306), prospective/retrospective studies (P = 0.470), quality of studies (P = 0.514), continent (P = 0.757), age of diagnosis (P = 0.283) and year of publication (P = 0.185) were not effective in the heterogeneity of studies. Sensitivity analysis by removing one study at a time indicated that the overall estimate is robust. Conclusion: According to the meta-analysis, SC (overall, elective, and emergency) increased the risk of childhood asthma. Therefore, it is hoped that developing clinical guidelines and implementing appropriate management plans would diminish the risk of asthma.