Child protective services are the primary agencies authorized by federal law and state policies to intervene with substance using pregnant women and new mothers. This dissertation argues that growing public acceptance of child welfare authority over American families (1950-1980) enabled legislators to expand professional surveillance of substance-using pregnant women (1980-2000). Drawing on archival, survey, legal, and professional journal data, the dissertation demonstrates how administrative shifts in the 1950s-1970s transformed child welfare from a sparsely staffed system broadly focused on a wide range of children’s issues into a sprawling multi-billion-dollar network of agencies narrowly focused on child maltreatment. As their focus narrowed, child welfare workers became increasingly concerned with assessing and preventing risk of child maltreatment. Combined with mandated reporting requirements and funding incentives that favored child removal over family preservation and poverty relief, a focus on risk functioned as a funnel effect, drawing multiple issues into the jurisdictionally contracted purview of child welfare over child maltreatment. As reports of substance-exposed infants grew in the late 1980s, an emphasis on risk assessment and maltreatment prevention enabled a professional framing of the substance-exposed infant as the paradigmatic case of a child at risk. Existing scholarship links regulation of prenatal substance use to the criminalization of poverty or to conservative anti-abortion efforts. These findings confound this narrative, showing that by the 1990s, public and professional opposition had doomed criminalization efforts to failure. Instead, both liberal and conservative legislators harnessed child welfare’s legitimation as a protective authority, committed to reducing maltreatment risks, with substance-exposed infants a paradigmatic example of a child at risk. Building on this bipartisan framing, legislators expanded child welfare authority in substance-exposed infant cases, while reframing family surveillance and child removal as supportive social service interventions.