Rural hospital volume and severe maternal morbidity risk

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According to a recent study published in JAMA Network Open, low- and high-risk obstetric patients experience increased risks of severe maternal morbidity (SMM) in lower-volume hospitals in rural counties.

Higher rates of maternal morbidity and mortality have been observed in the United States compared to other countries, with a 100% increase in maternal mortality compared to 1987 observed. Hospital characteristics, such as obstetric volume, have been associated with maternal health.

While a positive volume-outcome association has been found for conditions such as trauma and complex surgical procedures, there is little data on the impact for maternal outcomes. An association between hospital obstetric volume and decreased maternal health may impact future health policies, making it important to study this association.

To determine the association between obstetric volume and SMM in rural and urban hospitals in the United States, investigators conducted a retrospective, cross-sectional study. Linked vital statistics–patient discharge data was used in the analysis, with maternal and infant hospital discharge information gathered from certificate records of live births and fetal deaths.

Data from 2004 to 2018 was taken for California, data from 2004 to 2020 for Michigan, data from 2004 to 2014 for Pennsylvania, and data for South Carolina from 2004 to 2020. These locations included a variety of geography, health care systems, and sociodemographic characteristics.

Hospitals were categorized using location and metropolitan vs nonmetropolitan Urban Influence Codes. Urban hospitals were defined as those in metropolitan counties, while rural hospitals were in nonmetropolitan counties. 

A hospital-year was defined as, “the number of observations of annual birth volume and SMM rates (per hospital, per year).” In urban counties, there were 11,023,423 births across 5846 hospital-years from 2004 to 2020 included in the analysis, compared to 519,953 births across 1335 hospital-years in rural counties.

The primary exposure was hospital obstetric volume, measured using the number of births at 20 weeks or more of gestation observed in a calendar year. Stillbirths were included alongside livebirths, as SMM risk is greater among stillbirths. 

Categories for annual birth volume included low, medium, medium-high, and high. Low volume hospitals had 10 to 500 births, medium 501 to 1000 births, medium-high 1001 to 2000 births, and high over 2000 births in urban counties.

In rural counties, low volume hospitals had 10 to 120 births, medium 111 to 240 births, medium-high 241 to 460 births, and high over 460 births. Hospitals with under 10 births for half or more of the years evaluated were excluded.

Low or high risk of SMM was determined based on the presence of at least 1 clinical comorbidity. Of urban patients, 50.2% were low-risk, compared to 50.9% of rural patients. 

SMM, determined using International Classification of Diseases, Clinical Modificationcodes, was the primary outcome of the study. Covariates included primary payer at childbirth, maternal age, maternal race and ethnicity, and educational attainment.

Among urban counties, SMM incidence ranged from 0.73% in high volume hospitals to 0.50% in low volume hospitals, indicating decreased rates associated with lower hospital volumes. However, this association was not observed after adjusting for patient and hospital characteristics.

A lower average obstetric volume was observed among rural hospitals, as was a wide variation in SMM incidence. Rural hospitals with a high obstetric volume had an average SMM rate of 0.47%, compared to 0.70% in low volume hospitals. 

Adjusted risk ratios (ARRs) were 1.65 for low volume hospitals, 1.37 for medium volume, and 1.26 for medium-high volume. These ARRs indicated elevated risks compared to high volume hospitals.

Overall, lower volume hospitals had increased risks of SMM in rural counties. Investigators recommended rural counties receive quality improvement strategies designed for their communities.

Reference

Kozhimannil KB, Leonard SA, Handley SC, et al. Obstetric volume and severe maternal morbidity among low-risk and higher-risk patients giving birth at rural and urban US hospitals. JAMA Health Forum. 2023;4(6):e232110. doi:10.1001/jamahealthforum.2023.2110