Abstract
The gut microbiome develops in prenatal life and progresses through infancy and childhood. Identified factors that impact the quantity, quality, and diversity of the early gut microbiome include mode of delivery, early diet, environmental exposures, disease conditions, and treatment. Optimal gut health in childhood is impacted by microbiome stability and diversity. This narrative review provides an overview of the important factors including genetic, epigenetic, nutritional, and environmental exposures, playing a foundational role in establishing the early gut microbiome during the critical first "1000 days" of human life and its impact on pediatric obesity, allergy, and gastrointestinal disease.