Increases in Medicaid eligibility during the 1990s slightly increased the incidence of smoking during pregnancy, according to a new working paper by the National Bureau of Economic Research. The authors — Dhaval Dave of Bentley University, Robert Kaestner of the University of Illinois and George Wehby of the University of Iowa — cited their finding as one possible explanation for why the program failed to improve infant health outcomes.

“We find that increases in Medicaid eligibility were associated with increases in smoking and decreases in weight gain during pregnancy,” the authors wrote. “Raising Medicaid eligibility by 12 percentage points increased rates of any prenatal smoking and smoking more than five cigarettes daily by 0.7-0.8 percentage point.”