Aim: To evaluate the effect of nonsurgical periodontal therapy on clinical periodontal parameters in pregnant periodontitis study participants with and without gestational diabetes mellitus (GDM) and to estimate the changes in glycemic level in GDM study participants with periodontitis, before and after periodontal therapy. Materials and methodology: The present study is an interventional, prospective trial. A total of 120 study participants were selected. Each subject was randomly assigned to one of the four groups comprising 30 study participants in each group, based on the diagnosis of the disease. Group 1 included pregnant study participants with GDM with periodontitis, group 2 included pregnant study participants with GDM with periodontitis, group 3 included pregnant study participants with periodontitis, and group 4 included pregnant study participants with periodontitis. Periodontal therapy comprising of scaling and root planing followed by oral hygiene instruction was performed in group 2 and group 4, whereas only oral hygiene instructions were given in group 1 and group 3 in the study participants at baseline. Periodontal parameters and glycemic levels were reassessed before parturition. The study data was analyzed using Statistical Package for Social Sciences (SPSS) software V.22, IBM, Corp. for Windows. Results: The study showed a significant reduction in all the clinical parameters in both the groups following nonsurgical periodontal therapy, along with a reduction in glycemic levels. However, the results were better in group 2 as compared to all other groups. Conclusion: Nonsurgical periodontal therapy (NSPT) in pregnant periodontitis study participants with or without GDM showed better clinical results and a reduction in glycemic levels. Clinical significance: Improvement in periodontal clinical parameters and reduction in glycemic levels following nonsurgical periodontal therapy in GDM with periodontitis study participants.