In 2007, Australia introduced its most radical welfare reform in recent history, targeting Aboriginal communities with the aim of protecting children from harm. The ‘income management’ policy forced Aboriginal welfare recipients to spend at least half of their government transfers on essentials (e.g. food, housing), and less on non-essentials (e.g. alcohol, tobacco). By exploiting its staggered rollout, we estimate the impact of in utero exposure to the policy rollout on birthweight. We find that exposure to the income management policy reduced average birthweight robustly by 85 g and increased the risk of low birth weight by 3 percentage points. This finding is not explained by behavioral change (fertility, maternal risk behavior, access to care), or survival probabilities of at-risk fetuses. More likely, a lack of policy implementation planning and infrastructure led to acute income insecurity and stress during the rollout period, exacerbating the existing health inequalities it sought to address.