Early Life Exposures and the Development of the Infant Gut Microbiome: A Review

Abstract

The influence of the intestinal microbiota on metabolic, nutritional, and immunological processes is widely reported. With increasing literature associating altered microbial compositions with adverse health outcomes, it is important to understand how early life exposures may impact the development of gut microbial colonization and subsequent risk of altered metabolic and immune regulation. The purpose of this review is to describe factors in the maternal prenatal and perinatal period that may impact the intestinal microbiome over the first 2 years of life. A comprehensive search of MEDLINE, EMBASE, and the Cochrane Library using Medical Subject Headings (MeSH) and keywords for studies reporting on determinants of gut microbiota in infants (0 to 24 months) born at full term was conducted. Articles using culture techniques were included but not those that exclusively used molecular techniques that lacked sensitivity. Each citation title and abstract was independently assessed for inclusion for full text review. Findings related to the maternal prenatal period, mode of birthing, infant diet and antibiotics were included. Bifidobacteria and Bacteroides abundance were consistently greater in the first weeks of life in children born vaginally, and increased Bacteroides presence persisted throughout the first year. Bifidobacteria abundance was greater in breastfed children. Introduction of solid food was associated with greater presence of bacteria of the Firmicutes phylum. Although these studies advance our knowledge of how exposures in prenatal, intrapartum, and early life may impact colonization, larger studies with longitudinal follow-up are needed to improve our understanding of how perturbations may contribute to early origins of disease. This article has been peer reviewed.