The role of oral dysbiosis in pregnancy complications: a systematic review and meta-analysis of preterm birth.

Objective: To systematically review the association between oral dysbiosis and pregnancy-related complications and to quantitatively assess differences in oral microbial alpha diversity between preterm birth (PTB) and term birth (TB). Material and methods: A systematic search was conducted in July 2025 following PRISMA 2020 guidelines and registered in PROSPERO. Studies published between 2015 and 2025 assessing oral microbiota composition, alpha/beta diversity, or taxa abundance in relation to preeclampsia, gestational diabetes mellitus, preterm birth, low birth weight, mental health disorders, or pregnancy loss were included. Due to heterogeneity in study design, microbiome metrics, and outcome definitions, meta-analysis was restricted to studies comparing Shannon alpha diversity between PTB and TB. Study quality was assessed using the Newcastle-Ottawa Scale and the Joanna Briggs Institute checklist. Results: Twenty-one studies met the inclusion criteria, including cohort, case-control, and cross-sectional designs; four were included in the meta-analysis. Pregnancy complications were commonly associated with altered oral microbial profiles, characterized by reduced alpha diversity, changes in beta diversity, and increased abundance of genera such as Prevotella, Veillonella, and Porphyromonas. The meta-analysis suggested a directional trend toward altered alpha diversity in adverse pregnancy outcomes. Conclusions: Overall, the findings support a potential association between oral dysbiosis and pregnancy-related complications; however, this evidence is limited by the small scale and heterogeneity of the available studies. These results highlight the oral microbiome as a biologically plausible contributor to adverse maternal and neonatal outcomes and a promising focus for future mechanistic and translational research.