INTRODUCTION
UTERUS
The microbes that first colonize a neonate at birth play a key role in metabolic programming and immune system development (Cesarean section (C-section)—31.8% of all births in the United States in 2020 (Neonates delivered by C-section bypass the vaginal canal and therefore miss out on the exposure to the first live microbes and pioneer microbial colonizers that babies receive during vaginal birth, namely, the vaginal-perineal maternal microbes. Numerous studies confirm substantial differences in the microbiota acquisition and maturation in neonates delivered by C-section compared with vaginal delivery (C-section is correlated with other factors that could perturb the microbiota of the baby, including perinatal antibiotics, shorter gestational time, and lack of labor. No previous study has determined in a randomized, placebo-controlled trial, the effect of transplanting microbes via vaginal seeding to neonates that are extracted from the uterus into the air of operating rooms. In this double-blind, randomized, placebo-controlled study, we assess causation in the relationship between vaginal seeding of C-section-delivered babies and changes in the microbiome. We compare the fecal and skin microbiota of neonates randomly assigned to being seeded by their mother’s vaginal microbiome versus placebo seeding (control). We further assessed engraftment of maternal microbes in the infant microbiota by comparing the proportion of microbes shared between mothers and their children.