Modes of Cannabis Administration and Polysubstance Use among Women Before and During Pregnancy - PROJECT SUMMARY/ABSTRACT Importance of the proposed research. Prenatal cannabis use is increasingly common and could have largescale negative impacts on maternal and fetal health. Legalization of cannabis has led to the proliferation of new cannabis products with various modes of administration (e.g., vaping, edibles, dabbing blunts) that differ by THC potency and secondary exposures (e.g., nicotine, chemicals from vaping). Yet, we know little about how women use cannabis pre- and during pregnancy, whether modes vary with socio-demographics or local cannabis policies, or how modes relate to cannabis use frequency, cannabis use disorder (CUD), polysubstance use, quitting use in pregnancy, or adverse health outcomes. To fill this important gap in the literature, we will conduct an innovative mixed-methods study of ~310,000 racially and ethnically diverse pregnancies within Kaiser Permanente Northern CA (KPNC) from 2021 to 2026, where patients are universally screened for substance use as part of standard prenatal care via self-report and urine toxicology testing. Using rich electronic health record data and cannabis retailer and policy data, our study will examine socio- demographic and policy correlates of modes of use pre- and during pregnancy and test how modes relate to the risk of daily use, CUD, polysubstance use, substance use disorders (SUD), quitting pre- or during pregnancy, addiction treatment, and cannabis-related psychiatric and medical outcomes. With a focus on disparities, we will also examine differences in key associations by socio-demographic factors and test whether socio-demographic differences in continued cannabis use during pregnancy are mediated by differences in modes of administration. To gain further clinical insight and guide next steps, we will conduct interviews with pregnant women who used cannabis before and/or during pregnancy to understand factors influencing mode choice, perceived benefits/harms of different modes, changes in modes during pregnancy, and experiences with quitting. Findings will have immediate public health and clinical implications, providing critical information about the diverse ways in which women administer cannabis that could shift research and clinical practice paradigms. Results will also provide important data on whether local regulatory practices (e.g., cannabis retailer density, restrictiveness of local policies, warnings on prenatal use) are associated with variation in patterns of modes of cannabis use, informing the development of future regulations throughout the US. Finally, this unique study cohort will be a rich resource for future research on the impact of different modes of cannabis administration on fetal and neonatal outcomes.