Background: Despite research indicating that health, cost, and quality of care outcomes in midwife-led maternity care are comparable with and in some case preferable to those for patients with physician-led care, midwifery plays a more important role in some U.S. states than in others. However, this variability is not well-understood. Objectives: This study estimates the association between state scope of practice laws related to the autonomy of midwifery practice with the certified nurse-midwifery (CNM) workforce, access to midwife-attended births, and childbirth-related procedures and outcomes. Methods: Using multivariate regression models, we analyzed Natality Detail File data from births occurring from 2009 to 2011. Each state was classified regarding autonomous midwifery practice (not requiring supervision or contractual agreements) based on Lexis legal search. Results: States with autonomous practice laws had an average of 4.85 CNMs per 1,000 births, compared with 2.17 in states where CNM practice is subject to collaborative agreement. In states with autonomous CNM practice, women had higher odds of having a CNM-attended birth (adjusted odds ratio [AOR], 1.59; p =004), compared with women in states where midwifery is subject to collaborative agreement. In addition, women in states with autonomous practice had lower odds of cesarean delivery (AOR, 0.87; p =016), preterm birth (AOR, 0.87; p <.001), and low birth weight (AOR, 0.89; p =001), compared with women in states without such practice. Conclusions: States with regulations that support autonomous midwifery practice have a larger nurse-midwifery workforce, and a greater proportion of CNM-attended births. Correlations between autonomous practice laws and better birth outcomes suggest future policy efforts to enhance access to midwifery services may be beneficial to pregnancy outcomes and infant health.