- The use of electronic cigarettes (often referred to as vapes or e-cigs) has grown rapidly in the past decade. While these devices may not deliver the same level of carcinogens and toxicants as combustible cigarettes, they can deliver nicotine (a known developmental toxicant) as efficiently. Previous work suggests that, during pregnancy, women may supplement or completely substitute their combustible cigarette use with electronic cigarettes as either a form of harm reduction or smoking cessation aid. The use of this product during pregnancy raises concerns regarding the potential depression of combustible cigarette cessation during a time when women, historically, have been highly motivated to quit. Additionally, there may be risk for dual product use and increased and/or sustained nicotine exposure during fetal development. To date, little is known about the population-level prevalence of electronic cigarette use during pregnancy, what factors may be associated with electronic cigarette use during pregnancy, how electronic cigarette use behavior manifests among women during pregnancy (e.g., concurrently with combustible cigarettes or used exclusively), or how perinatal combustible cigarette use behavior manifests in the newly emerging electronic cigarette use landscape. The purpose of this dissertation was to examine combustible and electronic cigarette use before, during, and after pregnancy in a representative sample of recently pregnant women. To achieve this purpose, three analytic phases were conducted. All analyses used 2016 and 2017 Pregnancy Risk Assessment Monitoring System data. First, I described the prevalence of electronic cigarette use during pregnancy, as well as associated maternal characteristics. Results from this analysis indicate that, despite rapid increases in electronic cigarette use in the general population, only a small contingent of women were using these products during pregnancy. Electronic cigarette use was associated with maternal combustible cigarette use, education, race, ethnicity and prenatal depression. Second, I conducted latent class analysis to empirically identify patterns of combustible and electronic cigarette use before, during, and after pregnancy. Four classes were identified: 1) light combustible cigarette quitters (43.7% in 2016; 40.9% in 2017), 2) light combustible cigarette temporary quitters (17.6% in 2016; 19.5% in 2017), 3) persistent heavy combustible cigarette users (19.4% in 2016; 20.8% in 2017), and 4) persistent light combustible cigarette users (19.4% in 2016; 18.9% in 2017). Results from this analysis indicate that combustible cigarettes continue to be the primary product used among women, with light use (< 10 cigarettes per day) emerging as the predominant behavior pattern. Electronic cigarette use was minimal and was completely terminated during pregnancy in nearly all latent classes. Dual combustible and electronic cigarette use was not likely. Lastly, I conducted multinomial logistic regression to identify sociodemographic, pregnancy-specific, and mental-health-related factors associated with patterns of combustible and electronic cigarette use during the perinatal period. This analysis revealed that these factors varied significantly across combustible and electronic cigarette use patterns, with low socioeconomic status (low income and low education) continuing to be a persistent determinant of risky combustible cigarette use during pregnancy. This study sheds light on emerging patterns of combustible and electronic cigarette use behavior during a sensitive developmental period primed for behavior change. These patterns will continue to shift as new cohorts of exclusive electronic cigarette users enter adulthood and begin having children of their own, so continued surveillance of these behaviors during the perinatal period is imperative. Furthermore, despite, and perhaps as a result of, decades of tobacco control efforts, deeply embedded disparities continue to persist. To address these disparities, future efforts must consider perinatal product use at a more granular level and within the context of women’s lived experience.