Endometriosis and long-term risk of venous thromboembolism: a Danish nationwide study.

BACKGROUND AND AIMS: Endometriosis affects ∼10% of women of reproductive age. Emerging evidence suggests a link between endometriosis and systemic inflammation, potentially increasing the risk of venous thromboembolism (VTE), yet data on the association between endometriosis and VTE are lacking. The aim was to examine the association between endometriosis and long-term risk of VTE. METHODS: A nationwide, registry-based cohort study including all women with endometriosis from 1977 to 2024, matched 1:4 on birth and index year with women from the background population without endometriosis. The primary outcome was VTE as a composite of deep venous thrombosis and pulmonary embolism, while the individual components comprised the secondary outcomes. RESULTS: The study included 63 999 women with endometriosis and 255 996 matched female controls. At baseline, women with endometriosis had a higher burden of comorbidities, had greater use of medications, and more often had a history of abdominal/gynaecological surgeries. The incidence rate of VTE was higher in women with endometriosis [2.18 per 1000 person-years; 95% confidence interval (CI) 2.10-2.26] compared with controls (1.54 per 1000 person-years; 95% CI 1.51-1.58). In Cox regression analyses, endometriosis was associated with a significantly increased risk of VTE, even after adjustment for relevant comorbidities and use of hormonal contraception [unadjusted hazard ratio (HR) 1.43; 95% CI 1.36-1.50 and adjusted HR 1.52; 95% CI 1.42-1.63]. Similar results were observed for VTE subgroups: deep venous thrombosis alone (adjusted HR 1.50; 95% CI 1.38-1.63) and pulmonary embolism alone (adjusted HR 1.52; 95% CI 1.36-1.70). CONCLUSIONS: Endometriosis was associated with an increased long-term risk of VTE compared with a matched background population. These findings highlight the importance of clinical awareness and consideration of thrombotic risk in women with a history of endometriosis.