Each year, the U.S. spends $26.2 billion on costs associated with preterm birth — that’s birth before 37 weeks of pregnancy. Beyond the costs, babies born too early experience immediate and long-term problems, from developmental disabilities to asthma to hearing loss. For years, scientists have been studying possible environmental contributors, with many finding an association between preterm birth and air pollution. Earlier this week, a new study brought even more depth and clarity to this connection.