PROJECT SUMMARY Intrauterine exposure to maternal overweight/obesity and diabetes transmits risks to offspring, triggering a disease cycle across generations. Over half of US women have overweight or obesity at conception and ~10% of pregnancies are affected by diabetes, exposing nearly 2 million infants each year. Prenatal lifestyle interventions are well-studied, yet begin too late to impact the critical period of conception and early pregnancy. Starting interventions before conception may be key to halting the disease cycle. However, prior research is limited, often lacks offspring outcomes (especially sensitive measures), includes mostly white and affluent participants, and has been challenged to identify women likely to conceive soon. Further research is needed on scalable strategies to improve maternal-child health during preconception and early pregnancy, especially for racial and ethnic minority or low-income women with disparately high prevalence of obesity and diabetes. The National Diabetes Prevention Program (NDPP) is a widely-disseminated lifestyle intervention to reduce weight and glycemia that has untapped potential to improve maternal-child health. From an implementation science perspective, the NDPP has greater potential impact than new interventions that are unlikely to be scaled up, even if efficacious. We have delivered the NDPP to >1600 adults since 2013, including >350 young women. Our preliminary data shows that the NDPP may reduce peri-conceptional risks in diverse, low-income women. While limited engagement by younger women in the NDPP is a concern, strategies to increase engagement (motivational “pre-sessions”, remote delivery, and classes specially for young women) are promising. For example, young women attended our 12-month NDPP for 64 days longer after receiving a pre-session, with 2.0 kg/m2 lower preconception BMI and 0.4% lower A1c in early pregnancy, than controls. To plan a preconception trial, we also developed a 2-step screening protocol to 1) use electronic health record data (e.g., contraceptive use) to identify women who are more likely to conceive by 24 months (36% vs. 13% for all young women), and 2) outreach to confirm current family planning to expect ≥60% conception, based on our preliminary data showing that 73% conceived by 24 months if they endorsed intention to conceive or being sexual active without highly effective contraception. We propose a randomized controlled trial of an enhanced NDPP (NDPP-NextGen) initiated before pregnancy to evaluate effects on maternal-child health. We will recruit 360 women aged 18-39 years with overweight/obesity who are likely to conceive within 24 months. Women will be randomized to NDPP- NextGen or a usual care control group. Our specific aims are 1) to assess effects of NDPP-NextGen on peri- conceptional BMI and prenatal glycemia; 2) to assess effects of NDPP-NextGen on gestational weight gain and behavioral outcomes in pregnancy; and 3) to explore effects of NDPP-...