Covid-19 and the risk of pregnancy related venous thromboembolism; a register based cohort study

Introduction Pregnancy and the postpartum period are associated with an increased risk of venous thromboembolism (VTE) due to physiological hypercoagulability (1). COVID-19 is known to cause coagulopathy, but its impact on pregnancy-related VTE still leaves room for further research. The aim of our study was to investigate the association between COVID-19 during pregnancy and the postpartum period with VTE, and to evaluate the impact of infection timing and vaccination status. Methods Our nationwide register-based cohort study used Swedish population-based health registers during the COVID-19 pandemic to include a total of 234,729 women with singleton pregnancies who had a calculated day of birth between January 31, 2020, and March 8, 2022. The primary outcome was VTE, including deep vein thrombosis and pulmonary embolism, diagnosed during pregnancy or within 12 weeks postpartum. Hazard ratios (HRs) were calculated to assess the relative risk of VTE following COVID-19. Results Among the study population, 6,322 (2.7%) tested positive for SARS-CoV-2 during pregnancy and 1,310 (0.6%) during the postpartum period. VTE occurred in 33 infected women (0.4%) and 890 uninfected women (0.4%). A positive SARS-CoV-2 test was associated with increased VTE risk (hazard ratio HR 2.69; 95% confidence interval CI 1.72–4.22, p<0.001) especially within 21 days after infection (HR 9.74; 95% CI 5.49–17.26). Vaccinated women had a lower VTE incidence (0.3%) compared to unvaccinated women (0.5%). Conclusions COVID-19 during pregnancy and the postpartum period is associated with an increased risk of VTE, particularly in the first three weeks post-infection. These findings highlight the need for thrombotic risk assessment and thromboprophylaxis. The results also support the protective role of COVID-19 vaccination.