Volume as an Indicator for Outcomes for Severe Maternal Morbidity in the Military Health System

Background: Maternal obstetric morbidity is a growing concern in the USA, where rates of maternal morbidity exceed Europe and most developed countries. Prior studies have found that obstetric case volume affects maternal morbidity, with low-volume facilities having higher rates of morbidity. However, these studies were done in civilian healthcare systems that are different from the Military Health System (MHS). This study evaluates whether obstetric case volume impacts severe maternal morbidity (SMM) in military hospitals located in the continental United States. Methods: This cross-sectional study included all military treatment facilities (MTFs) (n = 35) that performed obstetric deliveries (n = 102,959) from October 2015 to September 2018. Data were collected from the MHS Data Repository and identified all deliveries for the study time period. Severe maternal morbidity was defined by the Centers for Disease Control. The 30-day readmission rates were also included in analysis. Military treatment facilities were separated into volume quartiles for analysis. Univariate logistic regressions were performed to determine the impact of MTF delivery volume on the probability of SMM and 30-day maternal readmissions. Results: The results for all regression models indicate that the MTF delivery volume had no significant impact on the probability of SMM. With regard to 30-day maternal readmissions, using the upper middle quartile as the comparison group due to the largest number of deliveries, MTFs in the lower middle quartile and in the highest quartile had a statistically significant higher likelihood of 30-day maternal readmissions. Conclusion: This study shows no difference in SMM rates in the MHS based on obstetric case volume. This is consistent with previous studies showing differences in MHS patient outcomes compared to civilian healthcare systems. The MHS is unique in that it provides families with universal healthcare coverage and access and provides care for approximately 40,000 deliveries annually. There may be unique lessons on volume and outcomes in the MHS that can be shared with healthcare planners and decision makers to improve care in the civilian setting.