Aspirin non-response in pregnant women at increased risk of pre-eclampsia

Objectives: Low dose aspirin (LDA) is recommended for women at increased risk of preeclampsia (PE), however it is not always effective. The study sought to determine the prevalence of non-response to LDA and to ascertain the effect of increasing aspirin dose in non-responders. Study design: Single centre, cohort study of 166 women at increased risk of PE was conducted in a large maternity unit in the UK between 2013 and 2016. All women were prescribed 75 mg of aspirin and invited to attend study visits at 18–24 weeks’ and 32–36 weeks’ gestation. Non-response was defined as a serum thromboxane B2 (TXB ₂) ≤10 ng/mL. Aspirin dose was increased to 150 mg if a bedside VerifyNow test suggested non-response (test value ≥ 550 arachidonic acid reactive units [ARU]) at 18–24 weeks. Adherence was assessed by self-report. Results: Based on serum TXB ₂, response rates were 85.3 % at 18–24 weeks and 79.3 % at 32–36 weeks’ gestation. Compared to serum TXB ₂, the VerifyNow test demonstrated moderate test performance (AUC 0.79 95 % CI 0.71−0.88, p < 0.0001) to detect non-response. High prevalence of non-adherence (6/10) was evident in persistent non-response group. Dose change from 75 to 150 mg of aspirin in adherent participants improved response (VerifyNow: 598 [95 % CI 550–665] ARU at 18–24 weeks on 75 mg aspirin, 509 [95 % CI 350–667] at 32–36 weeks on 150 mg of aspirin, [p < 0.0001]). Conclusions: Non-response to LDA is common in pregnancy but appears to be largely attributable to non-adherence. Dose change could be useful to improve response to LDA in this cohort.