ObjectivesThe Pregnancy Risk Assessment Monitoring System (PRAMS), conducted by the Centers for Disease Control and Prevention in collaboration with state health departments, is the largest state-level surveillance system that includes a question on the intention status of pregnancies leading to live birth. In 2012, the question was changed to include an additional response option describing uncertainty before the pregnancy about the desire for pregnancy. This analysis investigated how this additional response option affected women’s responses.MethodsWe used the change in the pregnancy intention question in 2012 as a natural experiment, taking advantage of relatively stable distributions of pregnancy intentions during short periods of time in states. Using PRAMS data from 2009-2014 (N = 222 781), we used a regression discontinuity-in-time design to test for differences in the proportion of women choosing each response option in the periods before and after the question change.ResultsDuring 2012-2014, 13%-15% of women chose the new response option, “I wasn’t sure what I wanted.” The addition of the new response option substantially affected distributions of pregnancy intentions, drawing responses away from all answer choices except “I wanted to be pregnant then.” Effects were not uniform across age, parity, or race/ethnicity or across states.ConclusionsThese effects could influence estimated levels and trends of the proportion of births that are characterized as intended, mistimed, or unwanted, as well as estimates of differences between demographic groups. These findings will help to inform new strategies for measuring pregnancy and childbearing desires among women.