Background <p>Gestational diabetes mellitus (GDM) alters maternal metabolism and the gut microbiota, thereby significantly affecting neonatal health. This narrative review synthesizes current clinical and translational evidence on temporal changes in the maternal gut microbiota across the three pregnancy trimesters in women with GDM and examines its subsequent impact on neonatal microbiome composition, immune development, and long-term disease risk.</p> Main body <p>GDM-associated dysbiosis has been reported early in pregnancy, but human evidence remains heterogeneous and does not establish direct vertical transmission; instead, maternal metabolic status and perinatal exposures may jointly shape early neonatal microbial patterns and immune–metabolic trajectories. These microbial alterations are closely associated with immune dysregulation and increased risks of inflammatory and metabolic disorders in offspring. Although diet, obesity, and probiotics influence microbial composition, their clinical efficacy in GDM remains inconsistent. Importantly, the available evidence remains heterogeneous, reflecting differences in cohort characteristics, sequencing methods, and study design, which limits definitive causal interpretation.</p> Conclusions <p>Advances in microbiota-based diagnostics and personalized microbial interventions—including microbiome-guided dietary modulation, targeted probiotic strategies, and metabolite-focused approaches tailored to individual maternal metabolic and microbial profiles—offer promising strategies to mitigate adverse outcomes by targeting the maternal–neonatal microbiome axis, highlighting microbiome-based approaches as an emerging translational direction.</p> Clinical trial number <p>Not applicable.</p> Graphical Abstract <p></p>