The prevalence of chronic immune non-communicable diseases (NCD) and obesity has increased during recent decades in Western societies. Epidemiologic studies suggest that birth by Cesarean section (CS) delivery increases the risk of the development of NCD and obesity later in life. The overall aim of this thesis was to assess the long-term impacts of the mode of delivery on child health and improve our understanding of the mediating mechanisms.

In this study, birth by CS delivery was associated with the development of asthma and allergic disease and obesity in early adulthood. The potential mechanism explaining the association may include aberrant microbial exposure at birth by CS. Moreover, this study revealed that CS delivery has an independent impact on breast milk microbiota composition at one month after delivery, suggesting that the aberrant microbial exposure related to birth by CS is not restricted to the perinatal period. Pregnancy is considered a pro-inflammatory state, and the composition of the maternal gut microbiota changes throughout pregnancy. In this study, the inflammatory-toned gut microbiota remained unchanged one month after delivery, and the concentrations of inflammatory cytokines continued to increase in the postpartum period, suggesting that the inflammatory tone continues beyond the perinatal period.

Birth by CS delivery is associated with the development of NCD and obesity later in life. Microbial depletion related to the delivery mode and aberrant breast milk microbiota composition, as well as increased exposure to antibiotics during early life, may be the mechanism in the developmental programming of child health. Future research should focus on supporting the development of a healthy gut microbiota composition in the child.