Certified Nurse‐Midwife Practice Authority as a Structural Determinant of Maternal Health

Policy Points State scope-of-practice restrictions on certified nurse-midwives are associated with lower workforce density and higher maternal vulnerability. In fact, 25 states currently impose collaborative or restricted practice environments that coincide with the nation's worst maternal health indicators. Mediation analysis revealed that 27% of the regulatory effect operates through workforce supply, whereas 73% reflects a direct policy effect, indicating that both regulatory reform and workforce investment are needed. Federal incentives through the Centers for Medicare and Medicaid Services's Rural Health Transformation Program now award scoring points based on state practice authority classifications, directly linking the state regulatory environment to federal funding and providing states with both an evidence-based rationale and a financial incentive for reform. CONTEXT: Certified nurse-midwives (CNMs) provide evidence-based maternity care associated with improved birth outcomes, yet half of US states do not grant them independent practice authority. State scope-of-practice regulations may function as structural determinants of maternal health by constraining both the midwifery workforce and the conditions under which care is delivered. Prior studies have documented associations between midwifery regulation and workforce availability but have not formally tested the mechanisms linking regulation to population-level maternal health outcomes. METHODS: We conducted a cross-sectional ecological analysis of all 50 US states, classifying each by CNM practice authority (independent, collaborative, or restricted) using American College of Nurse-Midwives state practice environment data (March 2026). CNM workforce density was calculated from American Midwifery Certification Board data (2022-2023). The primary outcome was the maternal vulnerability index (MVI), a composite of 43 indicators excluding provider density. The secondary outcome was March of Dimes preterm birth report card grades. We used one-way analysis of variance, multiple linear regression, and Baron and Kenny mediation analysis with Sobel tests and bias-corrected bootstrap confidence intervals to test whether workforce density mediated the relationship between practice authority and maternal vulnerability. FINDINGS: States allowing independent practice had significantly higher CNM densities than collaborative states (6.5 vs. 2.9 per 1,000 births, P < .001), as well as lower MVI scores (2.1 vs. 4.1, P < .001). The effect sizes were large (Cohen's d = 1.34 for CNM density, d = -1.62 for MVI). CNM density was found to mediate 26.7% of the practice authority-MVI association (Sobel z = -2.10, P = .036; 95% bias-corrected and accelerated [BCa] bootstrap CI [-0.88, -0.08]). The remaining 73.3% represented a direct policy effect that is not explained by workforce numbers. These results were robust to alternative classifications using nurse practitioner regulatory data. CONCLUSIONS: State CNM scope-of-practice regulations are a modifiable policy lever associated with both clinician workforce distribution and population-level maternal vulnerability. Both regulatory reform and complementary workforce investments are needed to address maternal health inequities.