Background: Diabetes during pregnancy, including gestational diabetes mellitus (GDM) and pre-gestational diabetes mellitus (PGDM), is associated with increased maternal morbidity. While both conditions pose risks, comparative data on maternal complications remain limited. This study compares maternal complications among non-diabetic pregnant women, those with GDM, and those with PGDM to identify differences in complication rates and inform risk-specific clinical care. Methods: This prospective cross-sectional observational study was conducted at Bangabandhu Sheikh Mujib Medical University (BSMMU) and BIRDEM Hospital, Dhaka, Bangladesh, from January 2004 to December 2005. A total of 150 pregnant women were enrolled and divided into three equal groups: Group A (non-diabetic), Group B (pregestational diabetes mellitus, PGDM), and Group C (gestational diabetes mellitus, GDM). Data were collected through questionnaires, clinical assessments, and medical records. Maternal complications during pregnancy, labor, and postpartum were recorded. Statistical analysis used SPSS, employing Chi-square and t-tests; p-values less than 0.05 were considered significant. Results: Maternal complications were significantly higher in diabetic groups (66% in GDM, 68% in PGDM) compared to non-diabetics (28%). Cesarean delivery was more frequent in PGDM (60%) and GDM (52%) than in non-diabetics (20%). Postpartum complications, particularly wound infection and endometritis, were more prevalent in the PGDM group. Intra-partum interventions, such as instrumental and operative deliveries, were also higher among diabetic pregnancies. Conclusion: Both GDM and PGDM significantly increase maternal complication rates, with PGDM posing a higher risk. Early screening, strict glycemic control, and multidisciplinary management are essential for improving maternal outcomes.