The gestational ecosystem: decoding mechanistic links between the maternal microbiome, obstetric outcomes, and offspring health: a narrative review.

Pregnancy is now recognised as a dynamic gestational ecosystem where maternal microbial communities influence maternal physiology, obstetric outcomes, and offspring health. This review synthesises recent advances in understanding the maternal microbiome's role in this process. We examine the spatial and temporal dynamics of the maternal microbiome, highlighting niche-specific remodelling in the gut, vagina, and oral cavity, and critically appraise the controversial evidence for a placental microbiome. We explore cutting-edge mechanistic pathways, including immunomodulation via short-chain fatty acids (SCFAs) and histamine, metabolic cross-talk through bile acids and neurotransmitters, vascular disruption via metabolites like trimethylamine N-oxide (TMAO), and the role of biofilm-associated infection. These pathways link microbial dysbiosis to adverse outcomes such as preterm birth, preeclampsia, and gestational diabetes. Furthermore, we detail how maternal microbes program offspring metabolic, immune, and neurodevelopmental trajectories through vertical transmission and metabolite-mediated epigenetic regulation. This review shows that the maternal microbiome is a modifiable axis that influences pregnancy outcomes and offspring health through immune, metabolic, and epigenetic pathways. Translation to practice will require stronger causal evidence, contamination-aware low-biomass methods, and carefully designed intervention trials, including next-generation probiotics, postbiotics, and precision lifestyle strategies.