Abstract

The maternal and infant microbiomes play pivotal roles in pregnancy outcomes, immune maturation, and early 
childhood development. Traditionally, the fetus was thought to develop in a sterile environment; however, 
evidence now suggests that maternal microbial communities influence fetal biology even before birth. Pregnancy 
induces profound shifts in the gut, vaginal, and oral microbiota, which in turn affect immune tolerance, nutrient 
metabolism, and fetal growth. Dysbiosis during gestation is associated with adverse outcomes, including preterm 
birth, low birth weight, and impaired immune development. After birth, maternal transmission of microbes 
through delivery mode, breastfeeding, and environmental exposure seeds the infant microbiome, which matures 
over the first three years of life. Early microbial colonization shapes immune function, neurodevelopment, and 
behavioral outcomes, with disruptions linked to conditions such as asthma, allergies, obesity, autism spectrum 
disorder, and mood-related disorders. Nutrition, antibiotics, and cesarean delivery are major modulators of 
microbial assembly. Methodological advances in metagenomics and multi-omics approaches continue to deepen 
insights into host–microbe interactions. This review summarizes the role of the microbiome in pregnancy and 
early child development, with emphasis on immune education, neurodevelopment, and potential therapeutic 
interventions, including probiotics, dietary strategies, and microbiome modulation. 
Keywords: Pregnancy microbiome, Infant gut colonization, Immune system development, Gut–brain axis, and 
early childhood health.