Because women undergo hemostatic changes in preparation for delivery, pregnant and puerperal women are more susceptible to venous thromboembolism. Investigating whether COVID-19 infection was linked to VTE during pregnancy or 12 weeks after giving birth while using (prophylactic or therapeutic) anticoagulants was the aim of this study.
All women in Sweden and Norway who gave birth after 22 gestational weeks and whose conception dates were between March 2020 and 2022 were included in this population-based register research. The exposure was a PCR-verified COVID-19 test, and the result was a diagnosis of VTE either during pregnancy or 12 weeks after giving birth. Women who tested negative and those who had never been tested were considered non-infected.
Overall hazard ratios were obtained using Cox regression models, which controlled for maternal factors and anticoagulant usage and included COVID-19 infection as a time-varying exposure. We calculated the time-specific risk of VTE in the first 2, 4, 8, 12, and 16 weeks after COVID-19 infection in order to assess if there was a specific elevated risk of VTE soon after testing positive for the virus.
Of the 323,868 subjects, 80 (0.2%) were diagnosed with VTE, while 46,048 (14.2%) developed COVID-19 during pregnancy. There was a greater incidence of VTE in pregnant women with COVID-19 than in those without the virus (4.9 vs. 2.9/1000 person-years; adjusted overall hazard ratio [aHR] 1.26, 95% Confidence Interval [CI] 0.80-2.00).
Within two weeks of infection, the risk was at its highest (aHR 4.63, 95% CI 2.71–7.90), but it continued to be high for 12 weeks after infection (aHR 1.86, 95% CI 1.17–2.94). Nearly, 6 (0.07%) were diagnosed with VTE during the postpartum period, and 8,515 (2.6%) had COVID-19 (aHR 5.17, 95% CI 2.50-10.69).
Despite the rarity of VTE following COVID-19 infection, the infection was linked to a higher risk of VTE throughout pregnancy and after giving birth, even when anticoagulant usage was taken into account.
Overall, even after controlling for anticoagulants, COVID-19 during pregnancy or the postpartum period was linked to an increased risk of VTE. Even though the absolute risk of VTE was low, these results should help determine each person's risk when determining whether preventive anticoagulants are necessary throughout pregnancy and after giving birth.
Reference:
Örtqvist, A. K., Söderling, J., Magnus, M. C., Urhoj, S. K., Håberg, S. E., & Stephansson, O. (2025). COVID-19 infection increases the risk of venous thromboembolism during pregnancy and the postpartum period. European Journal of Epidemiology. https://doi.org/10.1007/s10654-025-01268-z
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