Low Dose, High Impact: Acetylsalicylic Acid and Preterm Pre-Eclampsia Prevention in Rheumatic Disease

Objectives Pre-eclampsia (PE) is an important cause of maternal and neonatal morbidity and mortality, particularly when onset is preterm (<37 weeks gestational age). PE occurs in 1.6-2.6% of all Canadian pregnancies.[1] Patients with certain rheumatic diseases are at higher risk for PE, most notably SLE which confers a threefold increase in risk.[2] Other risk factors include nulliparity and metabolic conditions like hypertension and diabetes. Prophylactic low-dose acetylsalicylic acid (ASA) (81 or 162 mg daily) for high-risk pregnancies has been shown to reduce risk of preterm PE by 62%.[3] There are limited data on ASA use in pregnant patients with rheumatic diseases. We describe the baseline characteristics and incidence of preterm PE in patients with rheumatic diseases receiving ASA compared to those not receiving ASA. Methods Patients at 2 specialized Canadian clinics for pregnancy in rheumatic diseases were recruited to the Canadian Pregnancy and Rheumatic Diseases registry (CaPRIS) between July 2020-October 2025. Participants were 18 or older, pregnant or planning pregnancy, and had 1 or more rheumatic diseases. Preeclampsia risk was assessed and ASA was started by the treating rheumatologist or obstetrical provider, either 81mg or 162mg daily starting before 14 weeks gestational age (GA) until 36 weeks GA. Baseline characteristics and pregnancy outcomes were compared with Fisher’s exact test and Student’s t-test. Results We included 110 pregnancies and their baseline characteristics and outcomes (Table 1). Seventy-five patients (68%) received ASA; 35 patients (32%) did not. Patients on ASA were more likely to have SLE (p <0.01); 4 of 21 patients (19%) with SLE in our cohort developed pre-eclampsia. Patients not treated with ASA were more likely to have axial spondyloarthritis (p <0.01). Ten patients (13%) on ASA developed preterm PE while 3 patients (9%) not on ASA developed preterm PE (p=0.55). There was no difference in GA at delivery or fetal weight between the groups. Table 1. Baseline Characteristics and Pre-eclampsia (PE) Outcomes by Acetylsalicylic Acid (ASA) Use in Women with Rheumatic Disease Conclusion Guidelines recommend low-dose ASA for prevention of preeclampsia in pregnant patients at increased risk. 68% of patients with rheumatic diseases in our clinics met these criteria. Rates of PE and preterm PE were higher in this cohort than national averages. However, we did not observe a significant difference in rate of preterm PE for high-risk patients treated with ASA compared to low-risk patients. These data suggest that ASA is effective in mitigating risk of preterm PE in high-risk patients with rheumatic diseases and should be considered routinely in such patients. References [1.] Dzakpasu S. CMAJ 2024;196:E897-904. [2.] Clowse ME. Am J Obstet Gynecol 2008;199:127. [3.] Rolnik DL. N Engl J Med 2017;377:613-22.