Racial Disparity in Severe Maternal Morbidity Associated with Hypertensive Disorders in Washington State: A Retrospective Cohort Study.

Objectives: To evaluate the relationship between hypertensive (HTN) disorders and severe maternal morbidity (SMM). To understand whether there is differential prevalence of HTN disorders by race and whether the relationship between HTN disorders and SMM is modified by race and ethnicity.

Methods: We performed a retrospective cohort study using patient-level rates of SMM for pregnancies at all 61 non-military hospitals in Washington State from 10/2015 to 9/2016. Data were obtained from the Washington State Comprehensive Hospital Abstract Reporting System. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated to evaluate the association of HTN disorders and SMM (with and without transfusion) overall and by race. The population-attributable fraction of HTN disorders on SMM within each racial/ethnic group was calculated.

Results: Of 76,965 deliveries, 864 (1.1%) had any SMM diagnosis or procedure. All racial and ethnic minorities, except white and Asian, were disproportionally affected by preeclampsia with severe features (SF) and SMM. Overall, and within each racial/ethnic group, the SMM rate was higher among pregnancies with any HTN disorder compared to no HTN disorder (2.8 vs. 0.9%, OR 3.1, 95% CI 2.7-3.6). Race and ethnicity significantly modified the association. Overall and within each racial/ethnic group, there was a dose-response relationship between the type of HTN disorder and SMM, with more severe HTN disorders leading to a greater risk of SMM. The population-attributable fraction of HTN disorders on SMM was 20.6% for Black individuals versus 17.5% overall. The findings were similar when reclassifying transfusion-only SMM as no SMM.

Conclusions: In Washington, HTN disorders are associated with SMM in a dose-dependent fashion with the greatest impact among Black individuals.