P1185Association between estrogen-based contraceptive use and venous thromboembolism among females with inflammatory bowel disease: A target trial emulation

Background Both estrogen-based contraceptives and inflammatory bowel disease (IBD) increase venous thromboembolism (VTE) risk.1 As many young U.S. women who desire contraception use estrogen-based products,2 we evaluated the age-stratified VTE risk among females with IBD who initiated estrogen versus (vs) non-estrogen-based prescription contraceptives. Methods Using the IQVIA Pharmetrics Plus pooled health insurance claims database, we emulated a target trial using an active comparator new user design (Figure 1A). We identified US females ages 14-44 with IBD and excluded those with pro-thrombotic conditions and/or contraindications for estrogen-based contraceptives (Figure 1B). We estimated the absolute risk of VTE among females with IBD initiating estrogen-based vs non-estrogen-based contraceptives using a Kaplan-Meier estimator, addressing confounding via stabilized inverse probability of treatment weights and loss to follow-up via inverse probability of censoring weights. We censored individuals after 2 years of follow-up. We performed stratified analyses by age (14-24, 25-34, and 35-44). We generated cumulative incidence curves, contrasted weighted risks using risk differences, and calculated 95% confidence intervals. Results Among 6,162 contraceptive initiators, 45% started an estrogen-based subtype and 55% started a non-estrogen-based subtype. Following adjustment, there were no significant differences in baseline characteristics between groups. VTEs occurred in 70 women (1.14%) with a similar incidence between groups, overall and by age (overall: 1.23% for estrogen-based vs 1.06% for non-estrogen-based initiators; Standardized mean difference [SMD] 0.017; age 14-25: 0.91% vs 0.66, SMD 0.028; age 26-35: 1.30% vs 1.23%, SMD 0.006; age 36-44: 1.85% vs 1.23%, SMD 0.050). We found a VTE cumulative incidence of 5.6/1,000 person-years for non-estrogen-based contraceptive initiators vs 8.9/1,000 for estrogen-based initiators (Figure 2 A-D). While overall and age-stratified VTE risk differences did not significantly differ between groups, there was a numerically higher incidence in estrogen-based initiators in those age 36-44 (Figure 2 E-H). Conclusion We found no significant difference in VTE risk among females with IBD initiating an estrogen-based vs a non-estrogen-based prescription contraceptive. In those age 36-44, we saw a non-significant but numerically higher VTE incidence in the estrogen-based group, suggesting a need for further investigation regarding the safety of estrogen-based contraceptives among females with IBD over age 35. References: 1. Mahadevan U, Seow CH, Barnes EL, et al. Global Consensus Statement on the Management of Pregnancy in Inflammatory Bowel Disease. Clin Gastroenterol Hepatol 2025;23:S1-s60. 2. Brenner EJ, Zhang X, Long MD, et al. High Use of Estrogen-based Contraceptives in Young Women with Inflammatory Bowel Disease in the United States. Clin Gastroenterol Hepatol 2023. Conflict of interest: Dr. Brenner, Erica: I am supported by the IQVIA Pediatric Clinical Research Scholar Award through the University of North Carolina Children’s Research Institute and an American College of Gastroenterology Junior Faculty Development Award. Zhang, Xian: No conflict of interest Kappelman, Michael: Dr. Kappelman is a consultant for Eli Lilly and Takeda, holds shares in Johnson & Johnson, and has received research support from Janssen and Abbvie. Long, Millie: Millie Long reports consultant for AbbVie, BMS, Celltrion, Janssen, Intercept, Lilly, Pfizer, Prometheus, Takeda, and Target RWE and research support from Lilly, Takeda, and Pfizer. Wood, Mollie: No conflict of interest