Hospital birth volume and rurality: Associations with pregnancy outcomes among individuals with chronic hypertension

Chronic hypertension in pregnancy has doubled in prevalence over the past 15 years, but little is known about pregnancy outcomes at hospitals with different characteristics. We evaluated the association between hospital birth volume and rurality with risk of adverse pregnancy outcomes among individuals with chronic hypertension.

We conducted a population-based study using linked vital statistics and birth hospitalization discharge data from Michigan, Oregon, South Carolina (2008-2020), and Pennsylvania (2008-2018). We classified hospitals based on federal rural-urban county classifications and annual birth volume. The primary outcome was a composite measure of adverse pregnancy outcomes, including superimposed preeclampsia or eclampsia, severe obstetric morbidities, and fetal/neonatal morbidities. We used multivariable modified Poisson regression models with hospital fixed effects and robust standard errors to estimate the risk ratios (RRs) with 95% confidence intervals (CIs) for the primary outcome and the component outcomes for each hospital group compared with high-volume urban hospitals.

Among 106,991 births to individuals with chronic hypertension, the crude incidence of the primary adverse pregnancy outcome was highest in high-volume urban hospitals (49.5%) and lowest in low-volume rural hospitals (34.4%). Additionally, a higher proportion of individuals giving birth at high-volume urban hospitals had a high (≥10) obstetric comorbidity score (45% vs. 24-27% at rural and low-volume urban hospitals). After robust adjustment for clinical characteristics in regression models, however, no differences between hospital groups were evident. Among primary outcome components, only the risk of superimposed preeclampsia or eclampsia was higher in low-volume urban hospitals (adjusted RR: 1.21; 95% CI: 1.09-1.34) and medium-volume rural hospitals (adjusted RR: 1.26; 95% CI: 1.05-1.50).

Adverse pregnancy outcomes among individuals with chronic hypertension were largely similar across hospital volume and rurality groups, after accounting for differences in case mix. However, superimposed preeclampsia or eclampsia was highest at medium-volume rural and low-volume urban hospitals, suggesting potential opportunities for improved prenatal clinical management of chronic hypertension.