OBJECTIVE: To examine the association between state-mandated insurance coverage for in vitro fertilization (IVF) and the incidence of multiple birth while controlling for differences in baseline patient characteristics. METHODS: We conducted a retrospective cohort study using the Society for Assisted Reproductive Technology Clinic Outcomes Reporting System from 2007 to 2011 to examine the association between state-mandated insurance coverage for IVF and the incidence of multiple birth while controlling for differences in baseline patient characteristics. Analyses were stratified according to patient age and day of embryo transfer (3 or 5). RESULTS: Of the 173,968 cycles included in the analysis, 45,011 (25.9%) were performed in mandated states and 128,957 (74.1%) in nonmandated states. The multiple birth rate was significantly lower in mandated states (29.0% compared with 32.8%, adjusted odds ratio [OR] 0.87, 99.95% confidence interval [CI] 0.80-0.94). After stratification, this association remained statistically significant only in women younger than 35 years old who underwent transfer on day 5 (33.1% compared with 38.6%, adjusted OR 0.81, 99.95% CI 0.71-0.92). Among women younger than 35 years with day 5 transfer, the elective single embryo transfer rate was significantly higher in mandated states (21.8% compared with 13.1%, adjusted OR 2.36, 99.95% CI 2.09-2.67). CONCLUSION: State-mandated insurance coverage for IVF is associated with decreased odds of multiple birth. This relationship is driven by increased use of elective single embryo transfer among young women undergoing day 5 transfer.