Determinants and health effects of dynamic changes in e-cigarette use before, during, and after pregnancy - PROJECT SUMMARY/ABSTRACT Rapid rise in e-cigarette (EC) use or vaping has been observed in the past decade, most notably among young populations and women. As a result of perceived harm reduction, some exclusive combustible cigarette (CC) smokers who are pregnant or planning a pregnancy may switch to vaping or initiate dual use to reduce CC smoking. Among exclusive EC uses, some may quit or reduce vaping during pregnancy. Among dual users, dynamic changes may also occur during pregnancy including discontinuing vaping and/or smoking. Currently, there is limited research on maternal and infant health effects related to EC use during pregnancy. Even less is known about the health consequences of dynamic changes in EC use during pregnancy. Furthermore, the determinants of these dynamic changes in EC use have not been characterized. We propose a 2-year secondary data analysis to examine the dynamic changes in maternal EC use around the time of pregnancy (before, during, and after), the determinants of these changes, and their effects on maternal and infant health. We will use existing and new pending data from two large U.S. national studies with complementary data: 1) the Pregnancy Risk Assessment Monitoring System (PRAMS) with N=108,110 existing mothers in the phase 8 during 2016-2018 plus new mothers in phase 9 during 2019-2021, and 2) the Population Assessment of Tobacco and Health (PATH) Study with N=4,392 existing pregnancies in waves 1-4 during 2013-2017 plus new pregnancies in wave 5 during 2018-2019 and Adult Telephone Survey in 2020. Female participants reported their EC/CC use within the 3 months before pregnancy, during the last 3 months of pregnancy, and after pregnancy (postpartum). We will focus on the following dynamic changes in EC use: discontinuing, switching, and relapsing. Potential determinants include socio-demographics, pregnancy intention and characteristics, baseline EC use and product features, risk perception of EC use, concurrent substance use, and time of survey. Prenatal outcomes include gestational weight gain and gestational duration. Neonatal outcomes include small-for-gestational-age birth, mode of delivery, and length of infant hospital stay. Postpartum outcomes include breastfeeding and postpartum depression. Specific Aim 1 is to examine determinants of dynamic changes in EC use before, during, and after pregnancy. Specific Aim 2 is to assess health outcomes associated with dynamic changes in EC use before, during, and after pregnancy. We have received secondary data from both national studies, have examined distributions of key variables, and have run preliminary analyses to ensure sufficient statistical power for study aims. This innovative study can yield critical evidence to guide regulation of EC products.