Maternal Oral Microbiome Dysbiosis and Adverse Pregnancy Outcomes: Microbial Signatures, Inflammatory Pathways, and Clinical Evidence

Background/Objectives: Pregnancy is characterized by complex physiological, hormonal, and immunological changes that influence the oral environment and the microbial composition of the oral cavity. Emerging evidence suggests that maternal oral dysbiosis may be associated with systemic inflammatory responses and may potentially influence pregnancy outcomes. This systematic review aimed to evaluate the current clinical evidence regarding the association between maternal oral dysbiosis and adverse pregnancy outcomes, including preterm birth, low birth weight, and gestational complications. Methods: A systematic search of PubMed, Scopus, Web of Science, and Cochrane Library was conducted for studies published between January 2013 and September 2025. Observational studies and clinical trials examining the relationship between maternal oral dysbiosis or periodontal pathogens and pregnancy outcomes in pregnant women were included. Study selection was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines, and the review was prospectively registered in PROSPERO (CRD420261383855). Data were extracted on the study design, population characteristics, microbiological assessment methods, and reported pregnancy outcomes. Ten studies met the inclusion criteria of this review. Results: Seven of the ten included studies reported significant associations between the increased prevalence of periodontal pathogens, including Porphyromonas gingivalis, Fusobacterium nucleatum, and Prevotella intermedia, and adverse pregnancy outcomes, particularly preterm birth and low birth weight (LBW). Several studies have identified oral bacterial DNA in placental tissues, supporting the potential hematogenous microbial translocation pathways. However, heterogeneity in microbiological assessment techniques and study designs limits the comparability of the findings. Conclusions: Current evidence suggests that maternal oral dysbiosis may be associated with the inflammatory pathways linked to adverse pregnancy outcomes. Further prospective studies and standardized microbiome analyses are required to clarify the role of the oral microbiome in maternal and fetal health. Integrating oral health assessments into prenatal care may be an important strategy for improving maternal and neonatal outcomes.