In Mice, C-Section Births Linked to Less Developed Microbiota and Weight Gain: Mice born by Cesarean-section gained more weight and lacked dynamic microbiota development compared to mice born vaginally, a new study reports. C-section births circumvent natural exposure to maternal vaginal bacteria, and the results suggest that such bacteria play a crucial role in normal metabolic development. While C-section is a life-saving practice - needed in 10-15% of births to avoid risking the life of mother or child - delivery by C-section is often overused, with some regions using C-sections in more than 40% of births. Concurrent with an increase in C-section births, obesity and immune-related diseases including type 1 diabetes, allergies and celiac disease are also on the rise. What's more, preventive antibiotics, which are used in C-sections, have also been related to increased risk of these modern diseases. To further investigate the impacts of C-sections on weight gain and gut microbiota during early development, Keith Martinez and colleagues compared C-section born mice to vaginally born mice. The microbiome structure of mice born vaginally matured normally, while C-section mice showed no major changes in microbiome maturity or structure over the four weeks following weaning. Vaginally born rodents also demonstrated more bacteria associated with a lean body type. Overall, C-section mice had gained 33% more weight 15 weeks after weaning. Interestingly, the effects were more pronounced by gender; female C-section born mice gained 70% more weight. Future work may examine the effects of birth mode for other animals. The authors further note that since C-sections in humans involve perinatal antibiotics, they would expect a stronger effect.