Concerns have arisen regarding the long-term impacts of cesarean section (CS) on the health of offspring. One mechanism linking CS with later diseases is the hygiene hypothesis, based on the concept of different bacteria present in the newborns depending on mode of delivery. This early-life difference in bacteria acquisition could have lasting effects on offspring gut microbiota composition and related disorders. This review and meta-analysis were performed to determine whether an association exists between CS and overweight/obesity in offspring and to evaluate the strength of the possible association.
Relevant articles and abstracts were obtained from searches of PubMed, EMBASE, and Web of Science databases through June 2012. Studies were cohort or case-control investigations that examined the association of CS compared with vaginal delivery with overweight/obesity in childhood (3–8 years), adolescence (9–18 years), or adulthood (>19 years). Statistical heterogeneity across estimates was assessed by I2 statistics; values of 25%, 50%, and 75% indicated low, medium, and high heterogeneity, respectively. The primary analysis was to estimate the overall pooled OR for offspring delivered by CS versus vaginal delivery and specific pooled ORs for children, adolescents, and adults. Two-sided P < 0.05 indicated statistical significance.
Eight of an initial 2454 studies met the inclusion criteria along with 1 unpublished study, for a total of 7 cohort and 2 case-control studies. Overall, 10 childhood, 2 adolescence, and 3 adulthood estimates were included in the meta-analysis. The pooled OR of overweight/obesity for offspring delivered by CS compared with those born vaginally was 1.33 (95% CI, 1.19–1.48), with moderate to high heterogeneity (I2 = 63%) across the 15 estimates. Pooled ORs of overweight and obesity were 1.22 (95% CI, 0.99–1.50; I2 = 64%) and 1.37 (95% CI, 1.21–2.56; I2 = 45%; P for interaction = 0.33), respectively. The pooled OR for childhood overweight/obesity was 1.32 (95% CI, 1.15–1.51; I2 = 66%) across the 10 estimates. The pooled OR of overweight was 1.22 (95% CI, 0.99–1.50; I2 = 64%), and that for obesity was 1.40 (95% CI, 1.17–1.67; I2 = 50%; P for interaction = 0.31). The pooled ORs for adolescence and adult obesity were 1.24 (95% CI, 1.00–1.54; I2 = 0%) and 1.50 (95% CI, 1.02–2.20; I2 = 74%), respectively. The pooled ORs for male and female offspring did not differ significantly.
Compared with vaginal delivery, CS was associated with a 33% increased risk of later overweight and obesity in offspring. The underlying mechanism of this association is unclear, although the hygiene hypothesis is one possible mechanism. Future studies should examine the causal relationship between CS and obesity, particularly in adolescents and adults, and whether these associations have a common pathway with other health outcomes in offspring born by CS.
Institute of Reproductive and Child Health/Ministry of Health Key Laboratory of Reproductive Health and Department of Epidemiology and Biostatistics, School of Public Health, Peking University Health Science Center, Beijing, China