To promote use of progestogen therapy to reduce premature births in Ohio by 10%. The Ohio Perinatal Quality Collaborative initiated a quality improvement project in 2014 working with clinics at 20 large maternity hospitals, Ohio Medicaid, Medicaid insurers, and service agencies to use quality improvement methods to identify eligible women and remove treatment barriers. The number of women eligible for prophylaxis, the percent prescribed a progestogen before 20 and 24 weeks of gestation, and barriers encountered were reported monthly. Clinics were asked to adopt protocols to identify candidates and initiate treatment promptly. System-level changes were made to expand Medicaid eligibility, maintain Medicaid coverage during pregnancy, improve communication, and adopt uniform data collection and efficient treatment protocols. Rates of singleton births before 32 and 37 weeks of gestation in Ohio hospitals were primary outcomes. We used statistical process control methods to analyze change and generalized linear mixed models to estimate program effects accounting for known risk factors. Participating sites tracked 2,562 women eligible for treatment between January 1, 2014, and November 30, 2015. Late entry to care, variable interpretation of treatment guidelines, maintenance of Medicaid coverage, and inefficient communication among health care providers and insurers were identified as treatment barriers. Births before 32 weeks of gestation decreased in all hospitals by 6.6% and in participating hospitals by 8.0%. Births before 32 weeks of gestation to women with prior preterm birth decreased by 20.5% in all hospitals, by 20.3% in African American women, and by 17.1% in women on Medicaid. Births before 37 weeks of gestation were minimally affected. Adjusting for risk factors and birth clustering by hospital confirmed a program-associated 13% (95% confidence interval 0.3-24%) reduction in births before 32 weeks of gestation to women with prior preterm birth. The Ohio progestogen project was associated with a sustained reduction in singleton births before 32 weeks of gestation in Ohio.