Periodontal disease is one of the risk factors for certain systemic conditions. Retrospective and prospective studies showed that pregnant women with periodontitis have significantly higher risk to deliver preterm low birth weight infants (gestation period < 37 weeks, and birth weight < 2500 grams) and the risk increase as the periodontitis progressed during pregnancy. Periodontal disease could mediate this systemic effect through the action of periodontal pathogens and lipopolysaccharide increasing the production of prostaglandin and cytokine (physiologic mediators in parturition) which will trigger the delivery of preterm low birth weight infants. Periodontal therapy significantly reduces the rates of preterm low birth weight among women with periodontitis. It is concluded that periodontal disease is an independent risk factor for preterm low birth weight, and inclusion of oral prophylaxis procedure during pregnancy should be considered.