US welfare policy is governed by a labyrinthine set of laws that oversee program eligibility, enrollment procedures and the cash value of benefits received, some established at the federal level, and some delegated to the states. The delegation of the administration of US welfare programs to the states has created wide variations in overall program distributions, which ultimately has a substantial impact on state poverty levels, income inequality and the direct program benefits that people receive. Changes in welfare policy in the 1990s generated further variations in program distributions, which likely had profound implications for population health. This study aims to explain the wide variation in state preterm birth rates with reference to variations in state income and social support (the various laws establishing eligibility, enrollment and value of benefits for welfare programs). Specifically, the study will examine the contribution of variations in the five major welfare programs on state preterm birth outcomes: unemployment insurance, income support (AFDC/TANF), food assistance (SNAP & WIC) and Medicaid.