Background/Purpose: While the use of oral contraceptives in females with immune mediated inflammatory diseases such as rheumatoid arthritis (RA) is acknowledged as a risk factor for venous thromboembolism (VTE), the interaction between oral contraceptive use and RA is poorly understood. In a large population based study, we aimed to estimate RA attributable VTE risk in females using oestrogen contraceptives and/or on hormone replacement therapy (HRT).

Methods: Females registered with a general practice January 1999 to December 2018 were identified from the Royal College of General Practitioners Research (RCGP) and Surveillance Centre (RSC) database. Female RA patients and VTE outcome (composite of pulmonary embolism and deep vein thrombosis) were determined using previously validated algorithms. Female unaffected controls (UCs) were matched 4:1 with RA patients by current age (per year), calendar time, and years since practice registration using nearest neighbour matching with replacement. Absolute VTE rates over 20 years were compared in RA patients versus matched UCs overall and in two different subgroups defined by the use of oestrogen contraceptives or HRT. Relative VTE risk over the same period was estimated using Cox proportional hazards models adjusted for sociodemographic and clinical features and established VTE risk factors (BMI [body mass index], smoking status, alcohol use, reduced mobility evidence, thrombophilia, lower limb fracture and family history of VTE).

Results: A total of 82,082 female adults were included in this study, of whom 16,634 were RA patients and 65,448 UCs. Average
study follow up was 8.3 years (standard deviation [SD]=6.2 years). Female RA patients (mean age 58.3, SD 16.5; mean BMI 27.0, SD 5.9) were similar to matched UCs in their clinical characteristics. Compared to UCs, females with RA were less likely to receive oral contraceptives (RA n=545 [3.3%], UCs n=2,542 [3.9], p< 0.001) but more likely to receive HRT (RA n=752 [4.5%], UCs n=2,460 [3.8], p< 0.001). Unadjusted VTE events rates were consistently higher in females with RA compared to UCs (430.2 per 100,000 personyears [py], 95% confidence interval [CI]: 396.1, 466.3; UC: 260.5 per 100,000 py, 95%CI: 247.1, 274.4) and in those receiving and not receiving oral contraceptives and HRT. Overall, relative risk of VTE was 52% higher in females with RA compared UCs (adjusted hazard ratio [aHR]= 1.52, 95%CI: 1.36, 1.71, p< 0.001). Compared to UCs, relative risk increases were not statistically significant for females with RA receiving oral contraceptives (aHR 1.43; 95%CI 0.60, 3.63, p=0.46) and HRT (aHR 2.32; 95%CI 0.92, 5.85, p=0.08).

Conclusion: UK data suggest that all women with RA are at a similarly increased risk of VTE irrespective of the use of oestrogen contraceptives or HRT, but larger studies are needed to confirm this finding. It is therefore advisable to conduct routine VTE risk factor assessments for all females with RA.

This study was sponsored by Pfizer. Momentum Data UK provided project management, medical writing, and statistical support, funded by Pfizer.

This is an encore abstract previously presented/published for the British Society of Rheumatology Annual conference 2024 https://doi.org/10.1093/rheumatology/keae163.167

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/use-of-oral-contraceptives-in-females-with-rheumatoid-arthritis-is-not-associated-with-an-increased-risk-of-venous-thromboembolism-united-kingdom-population-based-study/