Background: Gestational diabetes mellitus (GDM) is a growing public health challenge associated with adverse maternal and neonatal outcomes. India contributes significantly to the global GDM burden, but comprehensive evaluations of demographic and lifestyle correlates in this population are limited.

Objectives: To assess clinical, demographic, and lifestyle risk factors associated with GDM in comparison with normoglycemic pregnant women in a Koshi Zone of Bihar tertiary-care setting.

Methods: A hospital-based case-control study was conducted between July 2023 and July 2025 among 240 pregnant women (120 GDM cases, 120 controls) between 22–32 weeks of gestation. Data on age, weight, BMI, occupation, gestational age, meal regularity, and sleep quality were collected using a structured proforma. Fasting blood glucose (FBG) levels were measured, and combined lifestyle behaviors were analyzed. Statistical analyses included independent t-tests and Chi-square tests with p<0.05 considered significant.

Results: Women with GDM had consistently higher BMI across gestational weeks, with significant differences at 25, 26, and 28 weeks (p<0.05). The 26–30 year age group carried the highest burden of GDM (58.3%) and exhibited higher BMI than controls (28.4 vs 27.1 kg/m², p=0.033). Women weighing >80 kg were twice as likely to have GDM compared to controls (16.7% vs 8.3%, p=0.003). Insomnia was more prevalent in GDM (41.7%) and associated with markedly higher FBG levels (224.0 vs 113.2 mg/dl, p<0.001). Lifestyle analysis revealed that poor sleep combined with irregular meals was significantly more common in GDM cases (30.0% vs 10.0%, p<0.001).

Conclusion: Elevated BMI, excess body weight, insomnia, and irregular meal timing are strongly associated with GDM in Koshi Zone of Bihar women. Sociodemographic profiling and early lifestyle interventions-including structured meal planning and sleep hygiene-may reduce the risk of GDM and improve pregnancy outcomes.