Marijuana is the most commonly used illicit substance under federal law in the United States (1); however, many states have legalized medical and adult nonmedical use. Evidence regarding the safety and health effects of cannabis use during pregnancy is largely inconclusive (2). Potential adverse health effects to exposed infants (e.g., lower birthweight) have been documented (2). To provide population-based estimates of use surrounding pregnancy, identify reasons for and mode of use, and understand characteristics of women who continue versus cease marijuana use during pregnancy, CDC analyzed data from eight states participating in the 2017 Pregnancy Risk Assessment Monitoring System (PRAMS) marijuana supplement. Overall, 9.8% of women self-reported marijuana use before pregnancy, 4.2% during pregnancy, and 5.5% after pregnancy. The most common reasons for use during pregnancy were to relieve stress or anxiety, nausea or vomiting, and pain. Smoking was the most common mode of use. In multivariable models that included age, race/ethnicity, marital status, education, insurance status, parity, trimester of entry into prenatal care, and cigarette and e-cigarette use during pregnancy, women who continued versus ceased marijuana use during pregnancy were more likely to be non-Hispanic white or other race/ethnicity than non-Hispanic black, be unmarried, have ≤12 years of education, and use cigarettes during pregnancy. The American College of Obstetricians and Gynecologists (ACOG) and the American Academy of Pediatrics (AAP) recommend refraining from marijuana use during pregnancy and lactation (3,4). Given the increasing number of states legalizing medical and adult nonmedical marijuana use, surveillance of perinatal marijuana use can inform clinical guidance, provider and patient education, and public health programs to support evidence-based approaches to addressing substance use.