This paper studies the effects of Secure Communities (SC), a wide‐ranging immigration enforcement program, on infant health outcomes in the United States. Using administrative birth certificate data together with event study and triple‐differences designs, I find that SC increases the incidence of very low birth weight by 21% for infants of foreign‐born Hispanic mothers, who were most likely to be affected by immigration enforcement. There is suggestive evidence that the results are consistent with (i) changes in maternal stress induced by deportation fear and (ii) inadequate prenatal nutrition. A back‐of‐the‐envelope calculation suggests that this unintended social cost of immigration enforcement ranges from $872 million to $1.59 billion annually.