Unravelling the Causal Relationship between Endometriosis and the Risk for Developing Venous Thromboembolism: A Pooled Analysis.

Objective:  To investigate the effect of endometriosis on venous thromboembolism (VTE) in oral contraceptive (OC) users. Pooled analysis on a harmonized dataset compromising international patient-centric cohort studies: INAS-VIPOS, INAS-SCORE, and INAS-FOCUS. Eleven European countries, the United States, and Canada. Individuals being newly prescribed an OC with or without an endometriosis and no VTE history.

Methods:  Detailed information was captured using self-administered questionnaires at baseline and every 6 to 12 months thereafter. Self-reported VTEs were medically validated and reviewed by an independent adjudication committee. Incidence rates (IRs) were calculated per 10,000 woman-years. The association of endometriosis on VTE was determined in a time-to-event analysis, calculating crude and adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) using stabilized inverse probability of treatment weighting (IPTW).

Results:  A total of 22,072 women had an endometriosis diagnosis, and 91,056 women did not. Women with endometriosis contributed 78,751 woman-years during which 41 VTE events occurred (IR: 5.2/10,000, 95% CI: 3.7-7.1) compared to 127 VTEs during 310,501 woman-years in women without endometriosis (IR: 4.1/10,000, 95% CI: 3.4-4.9). The hazard ratio of VTE in women with endometriosis was 1.79 (95% CI: 1.24-2.57) using stabilized IPTW controlling for age, body mass index, smoking, education, age at menarche, and family history of VTE. Subgroup and sensitivity analyses showed similar results.

Conclusion:  These results highlight the importance of considering endometriosis as a potential factor contributing to VTE in women using OC; however, further research on the relationship between endometriosis and VTE is warranted.