While maternal infections are a known risk for preterm birth, over 50% of spontaneous preterm deliveries are due to unexplained causes. Distant infections and inflammatory processes, including periodontal disease, could be one cause.79 The mechanisms of action for the interaction of periodontal disease and preterm birth may occur through two mechanisms.80
Women with periodontitis may experience more frequent bacteremias than periodontally healthy women, thus increasing the chance of periodontal bacteria being transmitted to the uterine environment. Once those bacteria are present within the uterus, they can elicit an immunoinflammatory cascade that may cause preterm birth. Pututive periodontal pathogens, including Porphrymonas gingivalis, Tannerella forsythia, Campylobacter rectus and Fusobacterium nucleatum have been identified in the amniotic fluid of subjects with preterm birth/low birth weight neonates.81-84 It has also been observed bleeding on probing (BOP) has a high association with preterm birth.85 Many of these pathogens have also demonstrated fetal growth restriction and spontaneous miscarriage in animal models.86,87 Potential for hematological transmission of periopathogenic bacteria from the oral cavity to the placental environment has been proposed.
The second mechanism involves the entrance of proinflammatory cytokines caused by periodontal inflammation into the systemic circulation. These cytokines, in turn, cause systemic inflammation inducing preterm birth. Periodontal disease, including periodontitis and gingivitis, is associated with inflammation both locally and systemically.76,88,89 This local and systemic inflammation could increase prostaglandin levels above the threshold for increased uterine contractility and induce preterm birth.
It has been suggested the risk for preterm birth is the highest when both of these proposed mechanisms occur at once and the fetus is exposed to periodontal bacteria and an immune response is generated.90 The specific mechanism of interaction is still not full elucidated and requires additional research.