Abstract: Intestinal microflora plays an important role in the whole life of human beings and the colonization of intestinal microflora in infants is critical for the formation of intestinal flora, which will affect their future growth, development and health. The purpose of this study is to explore the composition changes of intestinal microflora caused by delivery mode and its effects on the growth and development of 0-3 years old infants. In this study, 258 cases of intestinal fecal samples from healthy infants of 0-3 years old in Beijing were collected, including 97 caesarean section samples and 161 natural childbirth samples. The results by high-throughput sequencing technology showed that the relative abundance of some bacteria changed significantly. Compared with cesarean section group, the relative abundance of Actinobacteria (dominant bacteria, 13.92% VS 16.86%) and Acidobacteria (inferior bacteria, 0% VS 0.002 04%) in the intestine of natural childbirth infants increased significantly (P <0.05); and the relative abundance of Firmicutes (dominant bacteria, 67.17% VS 61.16%) and Tenericutes (inferior bacteria, 0.074% VS 0.051%) decreased significantly (P<0.05). At the genera level, the content of Bifidobacterium (13.01% VS 15.74%) in the dominant bacteria increased significantly in the intestinal feces of the natural childbearing infants, while Clostridium (2.25% VS 1.53%) decreased significantly. 

Key words: delivery mode, infants, intestinal microflora, age, BMI