Incidence and time trends of pregnancy-related first-time venous thromboembolism: a 33-year Swedish birth registry study

BACKGROUND: It is unknown whether changes in thromboprophylaxis recommendations are associated with decreasing incidence of pregnancy-related venous thromboembolism (VTE). OBJECTIVES: To investigate time trends in the incidence of pregnancy-related first-time VTE and fatal pulmonary embolism (PE) and to describe thromboprophylaxis use. METHODS: A nationwide register-based cohort study included all women who delivered a live or stillborn infant in Sweden from 1987 to 2019. Joinpoint analysis, featuring annual percent change (APC), was employed for time trend analysis in VTE incidence. RESULTS: The study included 3 449 885 deliveries, with 5202 women experiencing pregnancy-related first-time VTE and 18 fatal PEs. Incidence rates of first-time VTE, PE, and deep vein thrombosis (DVT) were 150.8/100 000 deliveries, 49.3/100 000 deliveries, and 101.5/100 000 deliveries, respectively. Time trend analysis showed an increase in pregnancy-related PE from 1987 to 2019 (APC, 4.9% [95% CI, 4.1%-5.9%]). DVT incidence increased from 1987 to 1993 (APC, 6.2% [95% CI, 0.9%-25.4%]), then decreased from 1993 to 2019 (APC, -0.5% [95% CI, -2.1% to -0.0%]). VTE incidence increased from 1987 to 1993 (APC, 5.5% [95% CI, 1.7%-22.3%]) and remained relatively stable thereafter (APC, 1.2% [95% CI, -4.3% to 1.7%]). Fatal PE varied between 0 and 2 annual cases. Prescriptions of low-molecular-weight heparins during pregnancy and postpartum increased from 2007 to 2018. CONCLUSION: During the study period, pregnancy-related PE increased, while DVT decreased from 1993 to 2019. Despite demographic shifts that might elevate VTE risk, the overall incidence of VTE remained stable, possibly because of the increased prescription of low-molecular-weight heparins.