A new study reveals that the incidence of neonatal abstinence syndrome — often caused by mothers using opioids during pregnancy — is increasing in the United States, and carries an enormous burden in terms of hospital days and costs. The number of US hospital admissions involving neonatal abstinence syndrome increased more than fourfold between the years 2003 and 2012. In 2012, neonatal abstinence syndrome cost nearly $316 million in the United States.