During normal pregnancy, the gut microbiota undergoes significant changes that may influence host metabolism. The study analyzed the gut microbiota of 91 pregnant women and their infants, revealing that the microbiota of mothers and infants become more similar with age, and the infant microbiota is not affected by the mother's health status. The gut microbiota changes dramatically from the first to the third trimester, with increased diversity, higher levels of Proteobacteria and Actinobacteria, and reduced richness. Third-trimester stool showed the strongest signs of inflammation and energy loss, but the microbiome gene repertoires remained constant across trimesters. When transferred to germ-free mice, third-trimester microbiota induced greater adiposity and insulin insensitivity compared to first-trimester microbiota. These findings suggest that host-microbial interactions can impact host metabolism during pregnancy, potentially benefiting the process. The study also found that the gut microbiota of third-trimester mothers was more diverse and showed greater variation compared to first-trimester microbiota. The microbiota of third-trimester mothers was also more similar to the microbiota of non-pregnant individuals with metabolic syndrome. The study highlights the importance of the gut microbiota in shaping host metabolism during pregnancy and suggests that changes in the microbiota may contribute to the development of metabolic syndrome. The results indicate that the gut microbiota plays a crucial role in the metabolic changes that occur during pregnancy, and that these changes may be beneficial in the context of a normal pregnancy.During normal pregnancy, the gut microbiota undergoes significant changes that may influence host metabolism. The study analyzed the gut microbiota of 91 pregnant women and their infants, revealing that the microbiota of mothers and infants become more similar with age, and the infant microbiota is not affected by the mother's health status. The gut microbiota changes dramatically from the first to the third trimester, with increased diversity, higher levels of Proteobacteria and Actinobacteria, and reduced richness. Third-trimester stool showed the strongest signs of inflammation and energy loss, but the microbiome gene repertoires remained constant across trimesters. When transferred to germ-free mice, third-trimester microbiota induced greater adiposity and insulin insensitivity compared to first-trimester microbiota. These findings suggest that host-microbial interactions can impact host metabolism during pregnancy, potentially benefiting the process. The study also found that the gut microbiota of third-trimester mothers was more diverse and showed greater variation compared to first-trimester microbiota. The microbiota of third-trimester mothers was also more similar to the microbiota of non-pregnant individuals with metabolic syndrome. The study highlights the importance of the gut microbiota in shaping host metabolism during pregnancy and suggests that changes in the microbiota may contribute to the development of metabolic syndrome. The results indicate that the gut microbiota plays a crucial role in the metabolic changes that occur during pregnancy, and that these changes may be beneficial in the context of a normal pregnancy.