Patterns of Aspirin Non-Use by Preeclampsia Risk Factors in High-Risk Pregnancies: A Retrospective Cohort Study

OBJECTIVES: Low-dose aspirin (acetylsalicylic acid [ASA]) prevents preterm preeclampsia, yet identifying who should initiate therapy remains challenging. We evaluated patterns of ASA non-use among high-risk pregnant patients with one or more preeclampsia risk factor(s) based on Canadian guidelines in a tertiary obstetrical centre in Ontario, Canada. METHODS: This was a retrospective cohort study of pregnant patients at high risk of placenta-mediated disorders who gave birth at a single tertiary centre from March 1, 2017, to December 31, 2019. We evaluated ASA non-use for individual preeclampsia risk factors and for cumulative risk factors using descriptive analyses and logistic regression. RESULTS: A total of 641 patients were included, 423 (66.0%) of whom did not use ASA. ASA non-use was prevalent among those with prior preeclampsia (33.6%), diabetes (47.1%), and chronic hypertension (45.0%). Risk factors with the highest non-use were nulliparity (76.0%), obesity (59.9%), and age >40 (58.6%). Cumulative risk factors had decreasing odds of non-use compared to no risk factors, although this reduction plateaued with ≥2 risk factors (odds ratio 0.14; 95% CI 0.07-0.27). Among all patients with an ASA indication based on current Canadian guidelines, 55.3% were not using ASA during their pregnancy. CONCLUSIONS: ASA non-use rates remain high among patients with significant risk factors for preeclampsia, including prior preeclampsia, diabetes, hypertension, obesity, and nulliparity. The presence of multiple risk factors is associated with minimal improvement in ASA use rates. Strategies are urgently needed to improve ASA use for preeclampsia prevention among high-risk pregnant patients.