Increased risk of subsequent antiphospholipid syndrome in patients with endometriosis

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.