We developed a composite index to quantify state legislation related to reproductive autonomy and examined its association with maternal and neonatal outcomes. We hypothesized that greater reproductive autonomy would be associated with lower rates of severe maternal morbidity (SMM), pregnancy-related mortality (PRM), preterm birth (PTB), and low birthweight. A Delphi panel was used to inform development of the index. Restrictive policies were assigned values of -1 and enabling policies +1. Publicly available data were used to conduct a cross-sectional study among all live births in the 50 U.S. states to people aged 15 to 44 between January 1, 2016, and December 31, 2018, to examine the association between the risk index and PRM, SMM, PTB, and low birthweight. We used linear regression with state scores and quartiles, adjusted for state-level proportions of White, Black, and Hispanic live births; percent living in rural areas; percent of population foreign born; Health Resources and Services Administration spending on maternal and child health; and the Opportunity Index, a composite measure of indicators of the economy, education, and community. From 2016 to 2018, there were 11,530,785 births, 2,846 pregnancy-related deaths, and 154,384 cases of SMM. The Delphi panel resulted in a summed state measure of 106 laws in 8 categories that could affect reproductive autonomy. In adjusted analyses, states in the most enabling (most reproductive autonomy) quartile had a 44.7 per 10,000 higher rate of SMM compared with the most restrictive quartile. However, the most enabling quartile was associated with a 9.87 per 100,000 lower rate of PRM and 0.67 per 100 lower rate of PTB compared with the most restrictive quartile (least reproductive autonomy). A composite policy index of reproductive autonomy was found to be associated with higher rates of SMM but lower rates of PRM and PTB. Further research is needed to understand how reproductive autonomy in the cumulative index may influence these and other maternal and birth outcomes.