(363) Hospital birth volume and rural/urban location: associations with perinatal outcomes among individuals with chronic hypertension

Objective: Chronic hypertension (cHTN) in pregnancy is increasing, but little is known about perinatal outcomes at birth hospitals with different characteristics. We evaluated the association between hospital birth volume and rural/urban location with risk of adverse perinatal outcomes among individuals with cHTN.

Study Design: We conducted a population-based study using linked vital statistics and birth hospitalization discharge data from Michigan, Oregon, Pennsylvania, and South Carolina (2008-2020). We classified hospitals based on federal rural-urban county classifications and annual birth volume. The primary outcome was a composite of obstetric and fetal/neonatal outcomes, with components as secondary outcomes (Table 1). We used multivariable modified Poisson regression models with hospital fixed effects and robust standard errors to estimate the relative risk (RR) of the outcomes for each hospital group compared with high-volume urban hospitals.

Results: Among 102,787 births to individuals with cHTN, the crude incidence of the primary outcome was highest in high-volume urban hospitals (47.2%) and lowest in low-volume rural hospitals (32.0%)(Table 2). Additionally, a higher proportion of individuals giving birth at high-volume urban hospitals had a high (≥10) obstetric comorbidity score (44% vs 24-26% at rural and low-volume urban hospitals). After robust adjustment in regression models, however, no differences between hospital groups were evident. Among primary outcome components, only risk of superimposed preeclampsia/eclampsia was higher in low-volume urban (RR: 1.14; 95% CI: 1.02-1.28) and medium-volume rural (RR: 1.33; 95% CI: 1.08-1.62) hospitals, with imprecise results in low-volume rural hospitals.

Conclusion: Lower rates of adverse outcomes among individuals with cHTN giving birth at lower volume and rural hospitals were observed and our results suggest these differences were largely explained by hospital case mix. Higher risk-adjusted rates of superimposed preeclampsia/eclampsia at medium-volume rural and low-volume urban hospitals suggest potential opportunities for prevention.