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Bulleted novelty statement:This historical cohort study examined the impact of gestational diabetes mellitus (GDM) after excluding pre-existing diabetes in mothers who delivered from 1981-2011 in Manitoba, Canada. First Nations (FN) women had 2-times more GDM and were 3-times more likely to develop postpartum diabetes than non-FN women. Postpartum diabetes in both FN and non-FN mothers was affected by GDM, lower family income and rural residence. The relative risk of developing postpartum diabetes in non-FN women was higher than FN women. The findings suggest that the reduction of GDM and socioeconomic inequities are required for preventing postpartum diabetes in FN and non-FN women.Running title: GDM and subsequent diabetes in mothers 2 Abstract Background: Over the past 30 years, the prevalence of diabetes has steadily increased among