Using the 2005-2014 waves of the American Community Survey –a period characterized by the rapid expansion of interior immigration enforcement initiatives across the United States, we evaluate the impact of a tougher policy environment on undocumented immigrants' fertility. We find that a one standard deviation increases in enforcement lowers childbearing among likely undocumented women by 5 percent. The effect emanates from police-based measures linked to increased deportations, which may raise uncertainty about the future of the family unit and its resources. Understanding these impacts is important given the critical contributions of immigrants and their offspring to diversity, the economy and the sustainability of the welfare state.