Prepregnancy smoking prevalence by state and data source among ART users, Massachusetts and Michigan 2008–2009. On Massachusetts’ birth certificate, prepregnancy smoking was determined from whether a woman reported smoking at least one cigarette daily in the year before pregnancy. On Michigan’s birth certificate, prepregnancy smoking was determined if a woman reported smoking before or during pregnancy and did not report a quit date or if a woman reported smoking before or during pregnancy and the quit date was 2 years before delivery year. In NASS, prepregnancy smoking was determined from whether a woman reported smoking at least 100 cigarettes in her lifetime and whether she smoked in the 3 months before pregnancy. The combined estimate of smoking was defined as women who reported smoking on BC, NASS, or both sources in the year before pregnancy, including records with unknown smoking status in one data source and known smoking status in the other data source. *Difference in prevalence estimates between birth certificate and NASS using two-way t-tests (p < 0.05). BC, birth certificates; NASS, National ART Surveillance System.