CONTEXT: The comparative efficacy of gestational diabetes (GDM) treatments lack conclusive evidence for choice of first-line treatment. OBJECTIVES: The aim of this study was to compare the efficacy of metformin and glibenclamide to insulin using a core outcome set (COS) to unify outcomes across trials investigating the treatment of gestational diabetes mellitus. STUDY DESIGN: A network meta-analysis (NMA) was conducted. DATA-SOURCE: PubMed, Embase, and Cochrane Controlled Register of Trials were searched from inception to January 2020. STUDY SELECTION: RCTs that enrolled pregnant women who were diagnosed with GDM and that compared the efficacy of different pharmacological interventions for the treatment of GDM were included. META-ANALYSIS: A generalized pairwise modelling framework was employed. RESULTS: A total of 38 RCTs with 6046 participants were included in the network meta-analysis. Compared to insulin, the estimated effect of metformin indicated improvements for weight gain (WMD -2·39 kg; 95% CI -3·31 to -1·46), maternal hypoglycemia (OR 0.34; 95% CI 0.12 to 0·97) and LGA (OR 0.61; 95% CI 0.38 to 0·98). There were also improvements in estimated effects for neonatal hypoglycemia (OR 0.48; 95% CI 0.19 to 1·25), pregnancy induced hypertension (OR 0.63; 95% CI 0.37 to 1·06), and preeclampsia (OR 0.74; 95% CI 0.538 to 1·04), though with limited evidence against our model hypothesis of equivalence with insulin for these outcomes. CONCLUSION: Metformin is, at least, comparable to insulin for the treatment of GDM. Glibenclamide appears less favorable, in comparison to insulin, than metformin.