Preterm birth (PTB), defined as delivery before 37 completed weeks of gestation, remains a major contributor to neonatal morbidity and mortality worldwide. Bacterial vaginosis (BV), characterised by disruption of the normal Lactobacillus-dominated vaginal microbiota and overgrowth of anaerobic bacteria, has been proposed as a potentially modifiable risk factor for PTB. However, the strength and consistency of this association remain uncertain. The aim of this study was to systematically review and quantitatively synthesise observational evidence on the association between BV and PTB in pregnant women using studies published between 2010 and 2026. A systematic review and meta-analysis were conducted in accordance with the PRISMA 2020 guidelines. Searches were performed in PubMed, Scopus, Web of Science, and DiVA. Study quality was assessed using the Newcastle-Ottawa Scale (NOS), and a random-effects meta-analysis was conducted using R statistical software. Ten observational studies involving 2,551,739 pregnant women from nine countries met the inclusion criteria. The pooled odds ratio was 1.81 (95% CI: 1.26–2.61; p = 0.005), indicating significantly higher odds of PTB among BV-positive women. Moderate heterogeneity was observed (I² = 44.5%; Q = 16.22; p = 0.063), and Egger's test showed no statistically significant evidence of publication bias (p = 0.398). Subgroup analysis demonstrated a weaker but still significant association in high-quality studies (NOS ≥7; OR 1.50, 95% CI: 1.04–2.16), while leave-one-out sensitivity analysis confirmed the robustness of the findings. Overall, BV was associated with an increased risk of PTB across diverse populations. However, the reduced effect estimates in higher-quality studies and inconsistent evidence regarding BV-targeted interventions suggest that the relationship may be more complex than a simple causal pathway. Further research should focus on standardised molecular diagnostic methods and targeted preventive strategies for women at greatest risk.