Did Medicaid Expansions Under the Affordable Care Act Increase the Use of Certified Nurse Midwives for Deliveries in the United States?

This study asks whether the Affordable Care Act’s Medicaid expansions led to greater use of Certified Nurse Midwives (CNMs) instead of physicians for childbirth. Using U.S. birth certificate data from 2010 to 2019, the authors compared states that expanded Medicaid to those that did not. They found that Medicaid expansions increased CNM-attended births by about one percentage point—an 11% rise—while physician-attended births declined by a similar amount. The increase occurred across both low- and high-risk pregnancies but was concentrated in states where Medicaid reimbursed CNMs at the same rate as physicians, suggesting that payment parity drives provider shifts.

The Policy Scientist’s Perspective

The article addresses an important policy issue: how large-scale public insurance expansions alter the composition of the healthcare workforce. Understanding these impacts is essential because expanding coverage does not automatically guarantee access if provider capacity is constrained. The study’s findings are timely as the United States continues to confront shortages of maternal health providers and widening disparities in access to obstetric care. The authors examine a nationally representative birth certificate dataset covering 2010–2019. Their event-study design is a credible causal inference strategy for policy implementation staggered across states and avoids many weaknesses of conventional regression-based approaches. The dataset’s completeness and temporal span enhance reliability, though underreporting of Certified Nurse Midwife deliveries may slightly bias results toward understatement. Overall, this is a careful and consequential contribution to the literature on workforce adaptation to health insurance expansions.

Full Citation and Link to Article

Beniwal, S., Hoehn-Velasco, L., & Jolles, D. R. (2025). Public health insurance expansions and non-physician providers: Evidence from Certified Nurse Midwives. Journal of Policy Analysis and Management, 1–38. https://doi.org/10.1002/pam.70032

Extended Summary

Central Research Question

This study investigates whether the Affordable Care Act’s (ACA) Medicaid expansions increased the use of Certified Nurse Midwives (CNMs) and Certified Midwives (CMs) for childbirth, thereby shifting the composition of obstetric care away from physicians. The authors focus on how public insurance expansions alter the balance between physician and non-physician providers in meeting rising healthcare demand. They also ask whether Medicaid reimbursement parity—states paying CNMs the same as physicians for comparable services—amplifies this shift. The question extends beyond maternal care to a broader issue of how supply-side dynamics adapt to large-scale changes in insurance coverage.

Previous Literature

The study builds on an extensive literature examining the consequences of public insurance expansions for healthcare utilization and provider behavior. Prior work has shown that Medicaid expansions under the ACA significantly reduced uninsurance rates, improved affordability, and increased healthcare use (Courtemanche et al., 2017; Sommers et al., 2016). Most of this research, however, has emphasized demand-side outcomes—how insurance expansions affect patient access—rather than how the provider landscape adjusts. A smaller but important body of work has examined supply-side responses, suggesting that higher demand for medical services can lead to increased adoption of technology and investment in human capital (Acemoglu & Finkelstein, 2008; Clemens & Gottlieb, 2017).

Several studies have looked specifically at non-physician providers (NPPs), such as nurse practitioners and physician assistants, showing that these professionals can substitute for or complement physician labor depending on reimbursement levels and scope of practice laws. For example, Kleiner et al. (2016) argued that physicians’ willingness to employ NPPs depends on whether they act as complements or substitutes for their services. Earlier research by Reinhardt (1972) and Brown (1988) posited that physicians underutilize delegation, even when doing so could raise efficiency. In the dental field, studies like Buchmueller et al. (2016) and Carey et al. (2020) found that Medicaid expansions led to greater use of dental hygienists as substitutes for dentists, showing similar patterns of workforce substitution under higher demand.

Within obstetrics, prior studies have examined CNMs as cost-effective and safe providers of maternity care, especially for low-risk pregnancies (Dubay et al., 2020; Wallace et al., 2024). CNMs provide care that often results in fewer cesarean sections, lower intervention rates, and similar or better maternal outcomes compared to physicians. Despite these benefits, CNMs remain underutilized in the United States, attending less than 10% of births—far below the rates in comparable high-income countries like the United Kingdom, where midwives attend over half of all births. Earlier work (Hoehn-Velasco et al., 2022; Markowitz et al., 2017) has shown that full practice authority and scope-of-practice reforms for CNMs increase their utilization, but these policies are distinct from the demand-side shifts caused by Medicaid expansions. The present paper thus fills a major gap in the literature by linking large-scale insurance coverage expansions to the workforce composition in obstetric care.

Data

The analysis relies on the Centers for Disease Control and Prevention’s (CDC) Natality Detailed Files, which contain birth certificate data for all U.S. births from 2010 through 2019. These data include detailed information on maternal demographics, risk factors, type of delivery, insurance coverage, and the provider type (physician, CNM/CM, or other midwife) recorded on the birth certificate. The authors restrict the main analysis to deliveries occurring in the mother’s state of residence to align the insurance context with the delivery setting.

Four main subsamples are used: (1) all deliveries, (2) low-risk first births (nulliparous, singleton, vertex presentations, without diabetes or hypertension), (3) low-risk subsequent births, and (4) high-risk deliveries (those involving multiple births, breech presentation, diabetes, or hypertension). Low-risk first births are the preferred analytic sample because they are most homogeneous and least affected by prior delivery experiences or selective sorting by mothers with known risk histories.

While the dataset provides comprehensive national coverage, the authors acknowledge key limitations. CNM/CM deliveries are known to be underreported on birth certificates (Biscone et al., 2017; Faucett & Kennedy, 2020), meaning that observed increases may understate the true effect. Insurance data are incomplete in early years because some states did not yet use the revised 2003 birth certificate format. However, the long time series, large sample size, and consistent coding across states make this an appropriate dataset for studying nationwide policy shocks.

Methods

The researchers use an event-study design to estimate how CNM/CM utilization changed before and after each state’s ACA Medicaid expansion. This approach compares states that expanded Medicaid between 2014 and 2016 (the “treatment group”) with those that did not expand during the study period (the “control group”). The outcome variable is the share of deliveries attended by CNMs/CMs. The analysis spans twelve quarters before and twelve quarters after each state’s expansion, allowing for visualization of pre-trends and dynamic post-treatment effects.

Formally, the event-study model includes state and quarter-year fixed effects to control for unobserved heterogeneity and national trends. State-level controls include age, marital status, unemployment, racial composition, education, rurality, and parity (for multiparous samples). Policy controls incorporate state scope-of-practice laws for midwives and licensing rules for Certified Professional Midwives (CPMs).

The authors estimate results using both traditional two-way fixed effects (TWFE) and the interaction-weighted estimator from Sun and Abraham (2021), which corrects for potential bias when treatment effects differ across cohorts in staggered adoption settings. Standard errors are clustered at the state level. The identification strategy assumes that, absent the Medicaid expansions, trends in CNM/CM use would have been parallel between expansion and non-expansion states. The authors verify this assumption empirically by showing flat pre-trends in CNM/CM utilization and by demonstrating that prior levels of midwife use do not predict expansion timing.

Several robustness checks are performed. The authors test specifications including state-specific linear trends, use both levels and logarithmic transformations of CNM/CM deliveries, add insurance and WIC participation controls, and run unweighted versions of the models. They also exclude states that enacted full practice authority for CNMs during the study period, ensuring results are not driven by other policy changes. Across all these tests, the estimated effects remain consistent.

Findings/Size Effects

The ACA Medicaid expansions increased the proportion of births attended by CNMs/CMs by roughly one percentage point, corresponding to an 11% relative increase. This rise was accompanied by a comparable decline in physician-attended deliveries, suggesting substitution rather than an overall increase in total deliveries. The timing of the effect begins about two quarters after the expansion and stabilizes thereafter, indicating a rapid supply-side response. The increase occurs across low-risk, high-risk, and all-birth samples, though it is strongest among low-risk first births.

Importantly, the rise in CNM/CM-attended deliveries occurs almost exclusively in states with Medicaid reimbursement parity—where CNMs receive the same payment rate as physicians for comparable services. In states lacking parity, the effect is negligible. This finding highlights reimbursement policy as a crucial mechanism enabling workforce substitution.

The authors find no evidence that the increase in CNM/CM deliveries resulted from migration of midwives into expansion states (an extensive-margin change). Instead, the rise reflects intensive-margin adjustments: existing CNMs/CMs worked more hours and earned higher salaries following the expansions. The increase is not explained by earlier prenatal care initiation, as CNM/CM-attended births rose across all levels of prenatal care timing, including those with no recorded prenatal visits.

The findings also suggest that CNMs/CMs increasingly handled spontaneous vaginal deliveries, while physicians specialized more in high-margin interventions such as cesarean sections. Consistent with this division of labor, the study finds small reductions in cesarean rates and small increases in induced deliveries for high-risk pregnancies, though changes for low-risk groups are minor. Overall, the results imply that health insurance expansions can reallocate labor toward cost-effective non-physician providers without reducing quality or access.

Conclusion

This study provides strong empirical evidence that Medicaid expansions under the ACA shifted obstetric care toward Certified Nurse Midwives and Certified Midwives, particularly in states that ensured reimbursement parity. The use of a rigorous event-study framework, supported by multiple robustness tests and dynamic treatment estimators, yields credible causal inference despite the observational nature of the data. The authors’ reliance on a decade of nationwide administrative records strengthens both internal and external validity, while the identified mechanisms—payment parity and intensive-margin labor responses—are theoretically and policy relevant.

The findings carry broader implications for healthcare workforce planning. As insurance coverage expands, the capacity of the healthcare system depends not only on the number of insured patients but also on the efficiency of provider deployment. By demonstrating that reimbursement policy can shape who provides care, this study underscores the importance of aligning payment structures with workforce availability. The results also suggest that other countries or U.S. states considering coverage expansions could face similar supply-side constraints and might benefit from integrating non-physician providers into care delivery more fully.

In sum, the paper offers a well-executed and policy-relevant contribution to the literature on the intersection of insurance design, labor economics, and health services delivery. Although not based on randomized experimentation, its methodological rigor and national scope make it one of the strongest recent empirical analyses of how insurance expansions reshape healthcare delivery at the provider level.