Insurance disruptions before, during, and after pregnancy are common in the United States, but little is known about the enrollment patterns of pregnant people in the Affordable Care Act Marketplaces. Data from the Pregnancy Risk Assessment Monitoring System from the period 2016-18 show that among respondents enrolled in Marketplace coverage, approximately one-third reported continuous Marketplace enrollment from preconception through the postpartum period. Compared with respondents who were continuously enrolled in Marketplace coverage from preconception through postpartum, respondents who enrolled in Marketplace plans during pregnancy had a 10.8 percent lower rate of adequate prenatal care, a 6.4 percent lower rate of timely prenatal care initiation, and a 13.2 percent lower rate of having twelve or more prenatal care visits. Policies that promote continuity of coverage during pregnancy, such as designating pregnancy as a qualifying event for a Marketplace open enrollment period, may enable pregnant people to enroll in Marketplace coverage early in their pregnancies and thus enhance access to prenatal care.