We report the effect of in-pregnancy periodontal care intensity on the risk of preterm low birthweight (PLBW) births, and the role of household income in this association. Only a few studies have examined the role of socioeconomic status (SES) in the relationship between prenatal periodontal care and risk of PLBW delivery under universal health care. This study adopted a population-based, case-control study using medical claims data in Taiwan. Mothers of PLBW and non-PLBW babies with livebirth deliveries between 2001 and 2005 (cases, n=20430 and controls, n=81573, respectively) were identified using the National Health Insurance Research Database (NHIRD) and matched. Periodontal disease and disease-specific (gingivitis and periodontitis) dental service utilization was calculated during gestational period and analyzed for its association with risk for PLBW delivery. Household income as proxy for SES was tested for modification effect. Prevalence of periodontitis and gingivitis was significantly higher in cases than in controls. Women who had these inflammatory conditions and sought treatment for either condition more frequently in gestation were at significantly lower risk for PLBW deliveries (periodontitis AOR: 0.757, 95% CI: 0.689-0.832; gingivitis AOR: 0.684, 95% CI: 0.582-0.805). Moreover, household income did not appear to be a significant effect modifier in the association between in-pregnancy periodontal/gingival care and PLBW delivery amongst study subjects. We found evidence that the intensity of disease-specific dental care during pregnancy acts as independent risk factor for PLBW delivery for periodontal and gingival women, and that the modification effect by SES was not evident under the context of universal health care system.