The effect of hospital acuity on severe maternal morbidity in high-risk patients

In 2015, the Society for Maternal-Fetal Medicine and the American College of Obstetricians and Gynecologists published guidelines that established levels of maternal care. These guidelines outlined the nursing, provider, and facility requirements for hospitals to be designated a birthing center or 1 of 4 levels of care. To date, these levels of maternal care have not been adopted widely; currently, no data exist on how these designations may affect maternal or neonatal outcomes.

Because the levels of maternal care attempt to reflect a hospital's ability to treat patients with certain conditions that are associated with increased risk of complications, our objective was to compare outcomes among high- and low-risk patients between high- and low-acuity hospitals. We hypothesized that hospitals that cared for a high rate of high-risk patients, which we considered "high-acuity" centers, would have a lower risk of severe maternal morbidity among high-risk patients compared with low-acuity centers.

Deliveries were identified in the 2013 Nationwide Readmission Database. A patient's comorbidity index was assigned based on diagnosis and procedure codes with the use of previously validated methods; a comorbidity index of ≥3 has been associated with increased odds of severe maternal morbidity. Patients were classified as low, intermediate, or high risk by their comorbidity index for analysis. Patients at hospitals with <100 deliveries per year and transferred patients were excluded. A hospital was defined as low or high-acuity if it was in the bottom or top quartile, respectively, based on its percent of patients with a comorbidity index of ≥3. Log-binomial regression models were constructed to assess the effects of a patient's comorbidity index group on the risk of severe morbidity in high- and low-acuity hospitals. The models controlled for available patient and hospital factors. The regression used patient-level data with robust standard errors that were clustered at the level of the hospital. The Wald test was used to assess for the effect modification between comorbidity index group and hospital acuity.

From 1203 hospitals, 1,656,659 delivering patients met the inclusion criteria. There were 58.7% low-risk, 39.0% intermediate-risk, and 2.3% high-risk patients in the overall sample, and the overall rate of severe maternal morbidity was 1.2%. Less than 3.7% of delivering patients in low-acuity hospitals had a high-risk condition. In comparison, >7.1% patients in high-acuity centers had a high-risk condition. In the adjusted analysis, intermediate-risk patients had a slightly increased risk of morbidity in both low-acuity and high-acuity centers compared with low-risk patients (adjusted risk ratios, 1.53 [95% confidence interval, 1.33-1.77] vs 1.57 [95% confidence interval, 1.49-1.65]). However, there was a notable difference in the adjusted risk ratios for severe maternal morbidity in the high-risk population: the adjusted risk ratio was 9.55 (95% confidence interval, 6.83-13.35) in low-acuity hospitals compared with 6.50 (95% confidence interval, 5.94-7.09) in high-acuity hospitals.

High-risk patients have a higher risk of severe maternal morbidity at low-acuity hospitals compared with high-acuity centers. These findings support the concept of regionalization of maternity care to improve outcomes for high-risk patients.