County-level Variation in Low Birthweight and Preterm Birth: An Evaluation of State Medicaid Expansion Under the Affordable Care Act

Abstract

Background: Rates of low birthweight and prematurity vary 2-fold across states in the United States, with increased rates among states with higher concentrations of racial minorities. Medicaid expansion may serve as a mechanism to reduce geographic variation within states that expanded, by improving health and access to care for vulnerable populations.

Objective: The objective of this study was to identify the association of Medicaid expansion with changes in county-level geographic variation in rates of low birthweight and preterm births, overall and stratified by race/ethnicity.

Research design: We compared changes in the coefficient of variation and the ratio of the 80th-to-20th percentiles using bootstrap samples (n=1000) of counties drawn separately for all births and for white, black, and Hispanic births, separately.

Measures: County-level rates of low birthweight and preterm birth.

Results: Before Medicaid expansion, counties in expansion states were concentrated among quintiles with lower rates of adverse birth outcomes and counties in nonexpansion states were concentrated among quintiles with higher rates. In expansion states, county-level variation, measured by the coefficient of variation, declined for both outcomes among all racial/ethnic categories. In nonexpansion states, geographic variation reduced for both outcomes among Hispanic births and for low birthweight among white births, but increased for both outcomes among black births.

Conclusions: The decrease in county-level variation in adverse birth outcomes among expansion states suggests improved equity in these states. Further reduction in geographic variation will depend largely on policies or interventions that reduce racial disparities in states that did and did not expand Medicaid.