Lower Preterm Birth Rates but Persistent Racial Disparities in an Open-Access Health Care System.

Background: The Military Health System (MHS) provides universal access to medical care to active duty service members, retirees, and their dependents. Observational data from small studies suggest lower preterm birth rates in the MHS compared with U.S. national averages. The objectives of this study are to determine the rate of preterm birth in the MHS from 2006 to 2012 compared with national rates and to analyze the impact of demographic factors on preterm birth in a universal access health care system.

Methods: A cohort of infants born in 2006-2012 was formed from the MHS M2 database. International Classification of Disease - Ninth Revision (ICD-9) codes were used to define prematurity. Preterm births were linked to military parent's demographic data. Calculated MHS preterm birth rates were compared with U.S. national data using the Pearson chi-square test and comparison via standardized differences. Logistic regression analyses were used to determine the impact of demographic factors on prematurity.

Findings: From 2006 to 2012, 564,920 infants were born in the MHS; 45,445 (8%) were born preterm. The preterm birth rate in the MHS peaked at 8.34% in 2008 and declined to 7.67% in 2012, which is significantly lower than the U.S. national average preterm birth rate over the same time period. In the 2008-2012 cohort, the odds of preterm birth were increased with Black race (adjusted odds ratio 1.30; 95% confidence interval 1.26-1.33) and with a parent of junior enlisted rank (adjusted odds ratio 1.08; 95% confidence interval 1.05-1.06), a surrogate for lower socioeconomic status. Odds of preterm birth were decreased in families with married parents and with an active duty mother.

Discussion: Preterm birth rates in the MHS have been consistently lower than national rates from 2006 to 2012, potentially due to universal access to health care. Black race increased odds of preterm birth despite universal access to health care. These findings support the need for further research examining racial disparities in health care outcomes related to preterm birth.