The aim of this paper is to descibe the pathogenic mechanisms that could explain the relationship between periodontitis and adverse pregnancy outcomes, and to review the evidence from systematic reviews and interventional studies, regarding the association between the clinical indicators of periodontitis and the incidence of low birth weight or preterm births. Preterm birth and low birth weight are world wide leading perinatal problems and have evident public health implications, due to the fact that their incidence doesn?t decrease in spite of the many attempts at their prevention. Both intrauterus infections and bacterial vaginosis of the mother are well known risk factors, but distant infections, even subclinicals, may also produce preterm births. Periodontitis is a chronic infection by anaerobic gram-negative organisms and may produce local and systemic infection, so a possible association between periodontitis and adverse pregnancy outcomes has been suggested. Since 1996, a number of studies have investigated the potential relationship between periodontitis and preterm and low birth weight. However, results have been controversial and more research is needed in order to confirm or discard this association.