Increased risk of subsequent antiphospholipid syndrome in patients with endometriosis

Abstract Background Although autoimmune abnormalities are common in patients with endometriosis, it is unknown whether patients with endometriosis have a higher risk of developing antiphospholipid syndrome (APS). Methods We conducted a retrospective cohort study by using the multi-institutional research network TriNetX from 1 January 2012 to 31 December 2021. A total of 13 131 782 women aged 20–60 years from networks within the USA were included. The risks of APS were compared between an endometriosis cohort and a non-endometriosis cohort in subgroup analyses by age, obesity and systemic lupus erythematosus (SLE), and the sensitivity analysis was stratified by the presence or absence of a history of surgery of the uterus. Results After 1:1 propensity score matching, the endometriosis and non-endometriosis cohorts each included 50 078 participants. Compared to individuals without endometriosis, patients with endometriosis had a higher risk of incident APS (log-rank test, P < 0.001). The hazard ratios (HRs) ranged from 1.82 [APS within 30 days to 1 year after the index date, 95% confidence intervals (CIs) 1.40–2.53] to 2.44 (APS within 30 days to any time after the index date, 95% CI 1.65–3.61). In the subgroup analyses, an increased risk of APS was observed in all ages, White race, and subgroups without smoking, obesity, asthma, inflammatory bowel disease and SLE (HR range 1.85–2.84). Sensitivity analyses revealed that the risk of APS increased in patients without surgery history of the uterus. Conclusions Patients with endometriosis had a higher risk (2.84-fold) of developing APS. Future large-scale prospective studies are warranted to confirm our results.