Intrinsic capacity impairment and modifiable associated factors among community-dwelling older adults with chronic diseases in China: a cross-sectional study.

The establishment of the gut microbiota during the early stages of life is a crucial process for maintaining overall human health. Initial microbial colonization of the neonatal gastrointestinal tract plays a fundamental role in the development of the immune system, metabolism, and brain function.

Any disruption in this process may contribute to adverse short- and long-term health consequences, including necrotizing enterocolitis (NEC), obesity, asthma, diabetes, inflammatory bowel disease, cancer, allergies, and neurological conditions related to the gut-brain axis. Over the past decade, some studies have suggested the potential presence of microbial communities in meconium and fetal tissues, supporting the hypothesis of in utero microbial exposure. However, these findings remain limited, methodologically challenging, and subject to ongoing debate. Current evidence indicates that, in the vast majority of healthy pregnancies, the neonatal gut microbiota is established primarily at birth, with maternal microbes acquired during delivery, as well as through early maternal-infant contact and initial environmental exposures representing the principal sources of early colonization. Nevertheless, maternal factors during pregnancy may influence fetal microbial and immune development indirectly, through multiple interconnected pathways, including the transplacental transfer of microbial metabolites, exposure via the umbilical cord or amniotic fluid, fetal membranes, and gastrointestinal tract. Evidence indicates that microbiome-related metabolites originating from the maternal microbiota are transferred vertically to the fetus. Short-chain fatty acids (SCFAs) and secondary bile acids appear to play active roles in modulating the fetal immune system and preparing the gut for postnatal microbial exposure.