The oral microbiome in relation to systemic maternal conditions and pregnancy complications: a systematic review and meta-analysis.

BACKGROUND: Alterations in the oral microbiome have been associated with systemic diseases, but evidence regarding maternal conditions and pregnancy complications remains limited. This systematic review evaluated these associations. METHODS: PubMed, Web of Science, and Embase were searched for studies using high-throughput sequencing to profile the oral microbiome in pregnant women with systemic diseases or adverse pregnancy outcomes. Random-effects meta-analyses were performed for alpha diversity indices, while methodological heterogeneity precluded quantitative synthesis of beta diversity and taxonomic abundance. RESULTS: Twenty-four studies were included, with 11 contributing to the meta-analysis. Gestational diabetes mellitus (GDM) was associated with lower Observed richness (SMD = -0.29, 95% CI: -0.55 to -0.03), whereas low birth weight (LBW) was associated with higher Chao1 (SMD = 0.46, 95% CI: 0.03-0.88). No significant alpha diversity differences were observed for pre-eclampsia or preterm birth. Differences in beta diversity and taxonomic abundance were reported across several conditions, although findings were heterogeneous. CONCLUSIONS: Oral microbial richness may be associated with GDM and LBW, but associations with other pregnancy complications remain uncertain. Standardized, large-scale prospective studies are needed.