Clinical Influence of Nonadherence With Prophylactic Aspirin in Preventing Preeclampsia in High-Risk Pregnancies

Aspirin nonadherence and its associated increase in cardiovascular and cerebrovascular events is well described; however, the prevalence of aspirin nonadherence among high-risk pregnant women at risk of preeclampsia and its influence on clinical outcomes remains unclear. Our study examined the prevalence of aspirin nonadherence and resistance among high-risk pregnant women quantitatively (platelet function analyzer 100 and plasma salicylic acid) and clinical outcomes relative to adherence. High-risk pregnant women were recruited across 3 centers in the South West Sydney Local Health District. Simultaneous clinic data, blood sample, and self-reported adherence assessment were prospectively collected at 4-week intervals from 12 to 36 weeks of gestation. Nonadherence was defined as normal platelet function analyzer 100 and nondetectable plasma salicylic acid in <90% of time points. Value of <90% is based on current data. Two hundred twenty women were recruited over 25 months. No woman was aspirin resistant, and 63 (44%) women demonstrated inadequate adherence. Women with inadequate adherence had higher incidence of early-onset preeclampsia (17% versus 2%; odds ratio [OR], 1.9 [95% CI, 1.1–8.7]; P =0.04), late-onset preeclampsia (41% versus 5%; OR, 4.2 [95% CI, 1.4–19.8]; P =0.04), intrauterine growth restriction (29% versus 5%; OR, 5.8; [95% CI, 1.2–8.3]; P =0.001), preterm delivery (27% versus 10%; OR, 5.2 [95% CI, 1.5–8.7]; P =0.008), and higher likelihood of increase in antihypertensives antenatally (60% versus 10%; OR, 4.6 [95% CI, 1.2–10.5]; P =0.003). Kaplan-Meier analysis demonstrated lower incidence of premature delivery in the ≥90% adherent group (HR, 0.3 [95% CI, 0.2–0.5]; P <0.001).Kappa coefficient agreement between qualitative and quantitative assessment of adherence was moderate (κ=0.48; SE=0.029; P <0.0001). Our data demonstrates that aspirin is an effective prophylactic agent with an absolute risk reduction of 51% (number needed to treat, 2) when adherence is ≥90%, compared with women with inadequate adherence. Women who were <90% adherent had higher rates of preeclampsia, intrauterine growth restriction, preterm delivery, and increase in antenatal antihypertensive requirements. Self-reported adherence does not accurately reflect actual adherence.