The goal of this proposed multi-center randomized clinical trial is to determine if non-surgical therapy for pregnant women with [periodontitis] reduces the incidence of preterm birth. As noted in the year 2000 Surgeon General's Report on Oral Health, preterm birth and low birth weight are the leading prenatal problems in the U.S. and it has been estimated that the annual costs associated with preterm birth total $5.4 billion. Despite significant efforts to prevent preterm birth, it remains a major cause of neonatal morbidity and mortality. Moreover, preterm birth is more likely to affect minority women who have disparities in health care. Human, animal, and bacteriologic studies have linked periodontal disease with preterm delivery and low birth weight and there are preliminary data indicating that periodontal therapy may reduce the incidence of preterm birth. After obtaining informed consent, this clinical trial will enroll [816 women] who are 13 to 16 weeks pregnant. Volunteers will be recruited from four populations in Minnesota, Mississippi, [Kentucky, and New York City (Harlem)] with high numbers of minorities and high rates of preterm birth. They will be randomly assigned to either a Test [n=408] or a Control [n=408] Group. Test Group subjects will receive non-surgical mechanical periodontal therapy. Control Group subjects will have periodontal therapy delayed until after delivery. All subjects will be monitored and treated as soon as possible if there is evidence of progressive periodontitis and all will receive essential dental care to restore caries and treat abscessed teeth. Maternal risk factors for preterm birth and/or intrauterine growth restriction will be used as covariates in the data analysis. Both Groups will be followed until delivery and the primary birth outcome variable will be gestational age at birth. [We will also document the effect of periodontal therapy on immune response, systemic markers of inflammation, periodontal infection and clinical periodontal measures.] If this study demonstrates that periodontal therapy has a positive effect in reducing preterm birth, it will have enormous public health implications in terms of neonatal mortality, morbidity and cost savings.