Background: Raised body mass index (BMI) and excessive gestational weight gain (GWG) are important determinants in development of gestational diabetes.Methods: A prospective, observational study carried out on antenatal women since their first trimester. These women were screened for gestational diabetes mellitus (GDM) by diabetes in pregnancy study group of India (DIPSI) criteria. All participants were followed up by measuring their BMI, weight gain, blood sugars in every trimester. Also, data was collected regarding any adverse outcomes.Results: Among all participants, 16.8% were diagnosed as GDM. 44% women of study group had weight gain beyond Institute of Medicine (IOM) recommendations. Higher risk of GDM was observed in women with raised BMI and excessive GWG. Also, odds of preeclampsia, preterm deliveries, caesarean section, macrosomia, intrauterine fetal death, neonatal intensive care unit (NICU) admissions were higher in women with GDM.Conclusions: Compliance of recommended weight gain during pregnancy have a strong impact on the fetal outcome. Amount and timing of weight gain plays a crucial role in GDM.