Impact of race on the incidence, diagnosis and outcomes of pregnancy-associated venous thromboembolism: A nested case-control study

Abstract Background: Venous thromboembolism (VTE) is a potentially life-threatening complication of pregnancy. While diagnostic delays are associated with worse prognosis, it remains unclear whether racialized individuals with pregnancy-associated VTE experience disparities in diagnostic workup and outcomes. We aimed to evaluate the care trajectory of patients with pregnancy-associated VTE with stratification by racial groups. Methods: We conducted a population-based, nested case-control study using administrative data holdings in Ontario, Canada. These datasets were linked using unique encoded identifiers and analyzed at ICES. We created a retrospective cohort of individuals with singleton deliveries (including stillbirths) from 2012 to 2023.We identified VTE cases up to 6 weeks postpartum based on a validated algorithm of diagnostic and imaging procedure codes. The main exposure was the birthing individual's self-reported racial group (Asian, Black, or White) recorded on their prenatal screening requisition. We first compared the incidence of pregnancy-associated VTE by racial groups. Individuals with pregnancy-associated VTE were then matched 1:10 to non-VTE controls by age, obstetrical comorbidity index, maternal body mass index, gestational age at index date, and delivery type within each racial group. We assigned the index date as date of VTE diagnosis among cases, and a pseudo-index date matched by gestational age among controls. We assessed healthcare visits in the 7 days preceding the index date (VTE diagnosis or matched pseudo-date) between cases and controls, with race as effect modifier. We then compared diagnoses provided during these visits by racial groups. Finally, we evaluated the effect of race on emergency department visits and hospitalizations in the 30 days following VTE diagnosis. Results: Among 442,816 pregnancies involving 305,326 birthing individuals (17.6% Asian, 6.5% Black, 75.9% White), we identified 1,793 imaging-confirmed VTEs (4.0 events per 1,000 pregnancies). Compared to White individuals, VTE incidence was lower among Asian individuals (adjusted risk ratio [aRR] 0.48, 95% confidence interval [CI] 0.41 – 0.57) and Black individuals (aRR 0.73, 95% CI 0.61 – 0.89). Among 1,769 VTE cases and 16,943 matched controls, VTE cases had a 17-fold increase in emergency department utilization in the 7 days prior to diagnosis [Poisson rate ratio 16.67, 95% CI 14.06 – 19.75]. While pre-diagnostic healthcare encounters were increased among cases across all racial groups, Asian and Black individuals were more likely have been discharged with a cardiorespiratory diagnosis during these encounters than White individuals (12.0% vs. 11.7% vs. 6.9% respectively, p=0.030). Emergency department visits in the 30 days after diagnosis were more likely among VTE cases across all racial groups, but disproportionately higher among Asian (odds ratio [OR] 10.6, 95% CI 6.8 – 16.6) and Black individuals (OR 12.3, 95% CI 7.4 – 20.7), compared to White individuals (OR 6.0, 95% CI 5.3 – 6.9; interaction p=0.003). Hospitalizations in the 30 days after diagnosis were increased among Black birthing individuals with VTE compared to matched controls (OR 2.90, 95% CI 1.70 – 4.97), whereas this was not observed among their Asian (OR 0.95, 95% CI 0.58 – 1.56) or White counterparts (1.12, 95% CI 0.96 – 1.25; interaction p=0.002). Interpretation: Individuals with pregnancy-associated VTE had a 17-fold higher rate of emergency department visits in the 7 days prior to imaging-confirmed diagnosis. The incidence of pregnancy-associated VTE was lower among Asian and Black birthing individuals compared to their White counterparts. However, Asian and Black birthing individuals with VTE had greater proportion of pre-diagnostic visits involving cardiorespiratory symptoms and higher unplanned acute care visits following their VTE diagnosis. These findings suggest potential missed opportunities for timely diagnosis and highlight racial disparities in quality of care for pregnancy-associated VTE.