• Mark A Clapp, Kaitlyn E James, Anjali J Kaimal, and Jamie R Daw.
• Deborah Kelly Center for Outcomes Research, Department of Obstetrics and Gynecology, Massachusetts General Hospital, and Harvard Medical School, Boston, Massachusetts; and the Department of Health Policy & Management, Columbia University Mailman School of Public Health, New York, New York.
• Obstet Gynecol. 2018 Dec 1; 132 (6): 1394-1400.

ObjectiveTo estimate the effects of the Affordable Care Act Medicaid expansion provision that was largely implemented in 2014 on preconception insurance coverage among low-income women.MethodsWe used a quasiexperimental, difference-in-difference design to compare changes in preconception insurance coverage among low-income women living in expansion compared with nonexpansion states before and after the Medicaid expansions. Women with family incomes 138% the federal poverty level or less who participated in the Pregnancy Risk Assessment Monitoring System from 2009 to 2015 from states that did or did not expand their Medicaid programs on January 1, 2014, were included. The exposure of interest was the state Medicaid expansion. The primary outcome was insurance status 1 month before conception. We conducted additional subgroup and sensitivity analyses to test the assumptions of the model and the robustness of the findings.ResultsThe study sample included 30,495 women from eight states that expanded Medicaid under the Affordable Care Act and 26,561 patients from seven states in that did not. The rate of preconception Medicaid coverage was 30.8% prepolicy and 35.6% postpolicy in nonexpansion states and 43.2% prepolicy and 56.8% postpolicy in expansion states. There was a significantly greater increase in Medicaid coverage in expansion states after the policy implementation (adjusted difference-in-difference estimate +8.6% points, 95% CI 1.1-16.0). Rates of preconception uninsurance were 44.2% prepolicy and 34.3% postpolicy in nonexpansion states and 37.4% prepolicy and 23.5% postpolicy in expansion states. There was no significant difference in the changes in uninsurance between the two groups in the postpolicy period (adjusted difference-in-difference estimate -4.1, 95% CI -11.1 to 2.9). Non-Medicaid insurance coverage was 25.3% prepolicy and 30.5% postpolicy in nonexpansion states and 19.4% prepolicy and 19.7% postpolicy in expansion states. Relative to nonexpansion states, there was a significant decrease in non-Medicaid coverage in the expansion states in the postpolicy period (adjusted difference-in-difference estimate -4.7, 95% CI -8.3 to -1.1). The results were robust to alternate model specifications and study period definitions.ConclusionMedicaid expansion was associated with increased enrollment in Medicaid before pregnancy among low-income women; however, there were no changes in the rates of uninsurance. Additional years of postpolicy data are needed to fully assess the effects of the policy change.

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