Background:The treatment of gestational diabetes mellitus (GDM) includes medical nutrition therapy (MNT), and insulin if MNT fails to achieve glycemic control. Limited data are available on predictors of insulin requirement in pregnancy and the difference in obstetric outcomes between the two treatment groups. This study was conducted with the primary objective of identifying predictors of antenatal insulin requirement and the secondary objective of comparing perinatal outcomes in MNT-treated versus insulin-treated groups.Methods: It was a prospective cohort study at a tertiary care institute in eastern India. Antenatal women were diagnosed with GDM as per the Diabetes in Pregnancy Study Group of India criteria and received MNT for 1 -2 weeks, depending on gestational age, followed by self-monitoring of blood glucose. Insulin therapy was added in those who could not meet the target blood glucose. Maternal and neonatal outcomes were studied in these two groups and an attempt was made to identify the predictors of antenatal insulin requirement. The perinatal outcomes in MNT-treated versus insulin-treated groups were also compared.Results: Data of 151 participants were analyzed. Eighty percent were controlled with MNT. Gestational age ≥ 33.28 weeks at diagnosis of GDM, maternal BMI ≥ 24.7 kg/m 2 and 75-gram oral glucose tolerance test (75-g OGTT) value ≥ 162 mg/dL were predictors of antenatal insulin requirement. The median age, weight, body mass index (BMI), value of 75-g OGTT at diagnosis of GDM, number of cesarean deliveries, gestational hypertension and neonatal hyperbilirubinemia were significantly higher in the insulin group. Conclusion:Gestational age at diagnosis of GDM, BMI and value of 75-g OGTT predicted antenatal insulin requirement. Gestational hypertension, rate of cesarean deliveries and neonatal hyperbilirubinemia were significantly higher in the insulin group.