[Truncated abstract] Periodontal disease is a common and underdiagnosed disease in humans that may have adverse effects on pregnancy outcomes. The aim of this thesis was to investigate the effects of periodontal disease in pregnancy by means of two observational human studies and the development of animal models of fetal and uterine exposure to periodontopathic bacteria and lipopolysaccharide. I performed a prospective study examining the rates of preterm birth, small for gestational age neonates and neonatal inflammation in 277 women who had undergone a detailed antenatal periodontal examination and oral health questionnaire. Periodontal disease was associated with small for gestational age neonates, and increased CRP levels in umbilical cord blood, but no effect was seen on the rate of preterm birth. Maternal oral health symptoms predicted both periodontal disease and newborn biometry. In a retrospective case control study, I examined the role of periodontal disease in perinatal mortality. Participants included 53 women who had experienced a perinatal loss for which no cause could be found after thorough investigation, and 111 control women. Women who had experienced a perinatal loss were more than twice as likely as controls to have periodontal disease. The incidence of periodontal disease was even higher in women in whom the perinatal loss was due to extreme prematurity. In contrast to my prospective study, risks to the pregnancy could not be predicted by maternal oral health behaviours or oral health symptoms. In order to better understand the mechanisms regulating the associations described in the human studies, two animal models were developed; one to investigate acute exposure and the second to investigate long-term exposure to periodontal pathogens. The first study examined the effects of administration of a bolus of periodontopathic bacteria and lipopolysaccharide to the pregnant sheep. Injection of bacteria and lipopolysaccharide in the amniotic fluid of the pregnant preterm sheep caused a high rate of fetal lethality, disturbance of fetal acid base status and inflammation of the fetus and membranes. Given the circumstances of exposure to periodontopathic pathogens in human periodontal disease, a model investigating long-term exposure to periodontopathic lipopolysaccharide on pregnancy outcomes was developed. ... Overall, I have demonstrated that maternal periodontal disease is associated with adverse pregnancy outcomes including fetal growth restriction and possibly perinatal loss. Mechanisms regulating these effects are likely to be mediated by fetal adaptations to intrauterine inflammation resulting in altered fetal development, growth or survival. Randomised controlled trials that are currently in progress will provide further information on the effects of periodontal disease in human pregnancy, and the efficacy of treatment to reduce these adverse outcomes.