PROJECT SUMMARY/ABSTRACT Women with a history of gestational diabetes mellitus (GDM) are at high risk of developing type 2 diabetes (T2DM). Evidence from the Diabetes Prevention Program (DPP) indicates that lifestyle change and metformin use in this population are clinically equivalent, each reducing the incidence of T2DM by approximately 50%; women with a GDM history thus face a preference-sensitive decision between these evidence-based alternatives. Shared decision making (SDM) is an attractive approach for addressing the patients’ choice between two alternatives, using a decision aid to make the decision explicit, describe the available options with equipoise, elicit patient preferences, and helping patients make an informed decision that is right for them. To our knowledge, there are no existing studies evaluating SDM for diabetes prevention among women with a history of GDM. Moreover, understading mechanisms of action of such an intervention will contribute to our understanding of the “how, why and for whom” this intervention is effective, in turn improving our ability to harness behavior change strategies to improve outcomes for women at high risk for T2DM, and increasing knowledge of how to aid behavior adoption and maintenance during and after similar diabetes prevention interventions. Our team has extensive experience with a team-based SDM approach for diabetes prevention, and our prior work showed that this approach leads to increased uptake of an evidence-based diabetes prevention strategy and sustained weight loss at 12-month follow-up in a broader population with prediabetes. In this administrative supplement, we aim to use new and existing data collected in the parent R01 to evaluate components of reflective motivation, based on the Capability, Opportunity, Motivation, and Behavior (COM-B) model of behavior, as mediators and moderators of the SDM intervention for diabetes prevention among women with a history of GDM within two health systems (UCLA and Intermountain). Our Specific Aims are as follows: To test components of reflective motivation (perceived risk, perceived control [locus of control + self-efficacy]) as modifiers of the effectiveness of an SDM intervention for diabetes prevention on primary (weight loss at 12 months) and secondary (physical activity, eating patterns, treatment engagement) outcomes among overweight/obese women with a GDM history and hemoglobin A1c between 5.7-6.4% enrolled in the parent RCT; and To test components of reflective motivation (patient activation) as mediators of the effectiveness of an SDM intervention for diabetes prevention on primary and secondary outcomes among women enrolled in the parent RCT. Our application presents a unique opportunity to study mechanisms of a robust behavior change intervention in an existing rigorous project addressing a critical area of unmet need in diabetes prevention for women with history of GDM, leveraging our health system infrastructure and our collaborativ...