Is elective cesarean section associated with a higher risk of asthma? A meta-analysis

Background: Recent meta-analyses indicate that children delivered by cesarean section have increased risk for asthma. However, the studies included in these previous meta-analyses showed significant heterogeneity. Furthermore, no previous meta-analysis has distinguished the association of elective and emergency CS, spontaneous and instrumental vaginal deliveries (VD) with the odds of asthma. Objective: To examine the association between specific mode of delivery and the prevalence of asthma. Methods: PUBMED, Google Scholar, EMBASE, and MEDLINE were searched to identify relevant studies. Odds ratio (OR) and 95% confidence interval (CI) were calculated from the prevalence of asthma in children born by elective CS, emergent CS, instrumental VD and spontaneous VD. Meta-analysis was then used to derive a combined OR. Heterogeneity between studies was also tested in the findings. Results: A total of 26 studies were identified. The overall meta-analysis revealed an increase in the risk of asthma in children delivered by CS (OR = 1.16, 95% CI 1.14, 1.29), and no evidence of heterogeneity was found (I-2 = 24.6%). Elective and emergency CS moderately increased the risk of asthma (OR = 1.21, 95% CI 1.17, 1.25; I-2 = 39.9%; OR = 1.23, 95% CI 1.19- 1.26). The risk of asthma was also higher in the children born by instrumental VD (OR = 1.07, 95% CI, 1.04- 1.11) but with evidence of heterogeneity (I-2 = 54.9%). Conclusion: About 20% increase in the subsequent risk of asthma was both found in children delivered by elective and emergency CS. The increasing rates of CS worldwide might partly explain the concomitant rise in asthma during the same time period.