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Highlights• Based on 5 years of real-world clinical register data, we report that the use of metformin in pregnancy was high among Indigenous women and has increased from 2012 to 2016 among non-Indigenous women with type 2 diabetes and gestational diabetes in a remote region of Australia. • We found no clear evidence of any adverse outcomes related to the use of metformin for the treatment of hyperglycemia in pregnancy. AbstractBackground: In Australia's Northern Territory, Indigenous mothers account for 33% of births and have high rates of hyperglycemia in pregnancy. The prevalence of type 2 diabetes (T2D) in pregnancy is up to 10-fold higher in Indigenous than non-Indigenous Australian mothers, and the use of metformin is common. We assessed birth outcomes in relation to metformin use during pregnancy from a clinical register.Methods: The study included women with gestational diabetes (GDM), newly diagnosed diabetes in pregnancy (DIP), or pre-existing T2D from 2012 to 2016. Data were analyzed for metformin use in the third trimester. Regression models were adjusted for maternal age, body mass index, parity, and insulin use. Results: Of 1649 pregnancies, 814 (49.4%) were to Indigenous women, of whom 234 (28.7%) had T2D (vs 4.6% non-Indigenous women; P < 0.001). Metformin use was high in Indigenous women (84%-90% T2D, 42%-48% GDM/DIP) and increased over time in non-Indigenous women (43%-100% T2D, 14%-35% GDM/DIP). Among Indigenous women with GDM/DIP, there were no significant differences between groups with and without metformin in cesarean section (51% vs 39%; adjusted odds ratio [aOR] 1.25, 95% confidence interval [CI] 0.87-1.81), *These authors contributed equally to this work.