Recent studies suggest a link between periodontitis and the Dietary Inflammatory Index (DII). We hypothesize that a more proinflammatory diet is associated with periodontitis risk in pregnant women with gestational diabetes mellitus (GDM). This study aimed to explore the association between DII scores and periodontitis risk in GDM women. In this cross-sectional study, 302 eligible GDM women from a Maternal and Child Health Hospital were enrolled between February and July 2023. DII scores were calculated based on dietary intake data collected using a validated semiquantitative food frequency questionnaire. Periodontal health was assessed through periodontal parameters including bleeding on probing, probing depth, and clinical attachment loss. Logistic regression models were employed to evaluate the odds ratios (ORs) for periodontitis risk across DII tertiles. Our study found that the prevalence of periodontitis across the DII tertiles 1, 2, and 3 was 34.7%, 56.4%, and 54.0%, respectively. Comparing the highest DII tertile (tertile 3) with the lowest (tertile 1), a significant association was found between higher DII scores and periodontitis risk (univariate OR: 2.21; 95% CI: 1.25, 3.90; P = .006), which remained significant in the fully adjusted model (adjusted OR: 2.30; 95% CI: 1.21, 4.37; P = .011). In conclusion, elevated DII scores are associated with an increased risk of periodontitis, underscoring the crucial role of a proinflammatory diet in periodontitis progression. Future well-designed experimental studies are needed to verify if tailored dietary strategies can effectively reduce periodontitis risk among pregnant women with GDM.