Objective To determine the association between the presence of periodontal pathogens and low birthweight. Methods This observational and case-control study consisted of mothers of infants weighing <2,500g (Group A), and mothers of newborns weighing ≥2,500g (Group B), born at Hospital da Mulher in Feira de Santana (BA), Brazil. A semi-structured questionnaire covering demographic data, gestational history and aspects related to general and oral health was employed postpartum. Following a complete periodontal examination, biofilm samples were collected at six sites in the mouth. The participants were further categorized in terms of presence or absence of periodontitis. Differences between the groups were determined using Pearson’s χ 2 test, odds ratio, and confidence intervals were obtained using the Mantel-Haenszel test. Results Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia and Prevotella intermedia were detected by polymerase chain reaction. A total of 303 postpartum women were evaluated, 224 (73.9%) in Group B. Statistically significant differences between the groups were found for age, body mass index and history of previous low birthweight babies. Group A had a higher frequency of periodontitis (33.34%) than Group B (16.22%). P. gingivalis and P. intermedia were detected more frequently among women with periodontitis (74.19% and 88.70%, respectively). Conclusion In this population, there was no association between the presence of maternal periodontal pathogens and the occurrence of low birthweight infants.