OBJECTIVE: The National Health Service Corps (NHSC) attracts clinicians to Health Professional Shortage Areas (HPSAs) through scholarships and loan repayments. Since 2009, the NHSC workforce, including maternity care clinicians, has substantially expanded. This study evaluates the association between NHSC expansion and prenatal care and birth outcomes. METHODS: In this quasi-experimental study, we adopted a generalized difference-in-differences design to compare changes in prenatal care and birth outcomes from 2005 to 2019 using birth certificate data. Counties designated as HPSAs without any NHSC maternity care clinicians throughout the study period were control counties, and those without such clinicians before 2009 but receiving them after 2009 were treated counties. Outcome measures include a count variable of number of prenatal visits and four dichotomous variables: prenatal care initiation in the first trimester, adequacy of prenatal care, preterm birth, and low birth weight. We estimated negative binomial models for number of prenatal visits and linear probability models for the dichotomous outcomes, adjusting for maternal characteristics, non-NHSC clinician density, and state-level policies. Stratified analyses were also conducted on the basis of birthing people's demographics and county-level characteristics. RESULTS: Our sample comprised 12,980,111 live births between 2005 and 2019 by individuals residing in 1,254 HPSA counties without any NHSC maternity care clinicians before 2009, including 222 counties that received such clinicians after 2009. Compared with control counties, pregnant people in treated counties experienced significant increases in prenatal visits (211 more prenatal visits relative to baseline of 11,226 visits per 1,000 births, P<.001) and in the likelihood of receiving adequate prenatal care (1.43 percentage point increase relative to baseline of 67.0 percentage points, P<.01). Although the NHSC expansion improved prenatal care use for all racial and ethnic groups, pregnant people residing in urban and high social vulnerability areas benefited most. Improvements in birth outcomes were observed only among certain subgroups such as a 0.91 percentage point reduction in preterm birth (relative to baseline of 12.6 percentage points, P<.001) and a 0.87 percentage point reduction in low birth weight (relative to baseline of 8.2 percentage points, P<.05) among pregnant people living in full-county HPSAs. CONCLUSION: The NHSC expansion since 2009 was associated with increases in prenatal care utilization, particularly among vulnerable populations. Although improvements were not observed in birth outcomes overall with NHSC expansion, modest reductions were observed in preterm birth and low birth weight in subsets of the population.
