Association Between Periodontopathogenic Bacteria and Preterm Birth Among Postpartum Women with Periodontitis: A Cross-Sectional Molecular Study from the Democratic Republic of the Congo

Background Periodontitis has been increasingly associated with adverse pregnancy outcomes, including preterm birth, through mechanisms involving periodontal dysbiosis and systemic inflammation. However, evidence regarding the contribution of specific periodontopathogenic bacteria remains limited, particularly in sub-Saharan Africa. Methods A cross-sectional study was conducted among postpartum women attending the University Clinics of Kinshasa from November 2025 to March 2026. Periodontal status was assessed using the 2018 classification of periodontal and peri-implant diseases and conditions. Sociodemographic, obstetric, and periodontal data were collected through interviews, medical record reviews, and comprehensive periodontal examinations. Subgingival plaque samples were collected from the deepest periodontal sites, genomic DNA was extracted, and six major periodontopathogenic bacterial species were detected by SYBR Green-based quantitative real-time polymerase chain reaction (qPCR). Associations between bacterial detection, severity of periodontitis, and preterm birth were evaluated using univariate and multivariable binary logistic regression. Results A total of 87 mothers were included in the study. Stage 2 (moderate) periodontitis was the most prevalent form of disease. The most frequently detected bacterial species were Fusobacterium nucleatum (91.9%), Porphyromonas gingivalis (78.1%), Tannerella forsythia (77.0%), and Treponema denticola (72.4%). Stage 3 (severe) periodontitis was significantly associated with birth outcomes (p = 0.02). Although no significant association was observed between individual bacterial species and severity of periodontitis, multivariable binary logistic regression identified Tannerella forsythia as an independent predictor of preterm birth (adjusted OR = 6.69, 95% CI: 1.22–36.61). Conclusions This study could provide novel molecular epidemiological information on the association between Tannerella forsythia and preterm birth among postpartum women with periodontitis in the Democratic Republic of the Congo. These findings suggest that the contribution of periodontal pathogens to adverse pregnancy outcomes may depend on the pathogenic potential of specific bacterial species rather than their presence in the subgingival biofilm.