Unauthorized immigration is one of the most contentious policy issues in the United States. In an attempt to curb unauthorized migration, many states have considered restrictive laws intended to make life so difficult for unauthorized immigrants that they would choose to leave the country. Arizona's Senate Bill 1070, enacted in 2010, was a pioneering example of these efforts. Using population-level natality data and causal inference methods, we examined the effect of SB1070 on infants exposed before birth in Arizona. Prenatal exposure to the bill resulted in lower birth weight among Latina immigrant women, but not among US-born white, black, or Latina women. The decline in birth weight resulted from exposure to the bill being signed into law, rather than from its (limited) implementation. The findings indicate that the threat of a punitive law, even in the absence of implementation, can have a harmful effect on the birth outcomes of the next generation. © The Author(s) 2018. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: [email protected].

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