 In order to address these knowledge gaps, the study will assemble and longitudinally follow a large, diverse birth cohort of approximately 420 individuals to determine the relationship between 1 antibiotic exposure and microbiome development; 2 antibiotic exposure and weight gain; and 3 microbiome development and weight gain. To accomplish this, the study will examine routine intrapartum, neonatal, and infant antibiotic exposures; use bacterial taxonomic marker gene sequencing, metatranscriptomics, and metabolomics to measure antibiotic-related shifts to the microbiome taxonomic carriage, biodiversity, and rate of maturation of the infant gut microbiome; and perform comprehensive, serial anthropometric measurements to assess weight gain and adiposity over the first 24 months of life. 