Aspirin to prevent preeclampsia: When to start and how much to give?

Empirical use of aspirin to prevent myocardial infarction dates back to 1950. It would take another 20 years for Sir John Vane to describe aspirin’s primary mechanism of action, inhibition of cyclooxygenase, for which he shared a Nobel Prize. In 1975 aspirin’s inhibitory effect on platelet-induced arterial thrombosis was described by Weiss and associates. Later studies showed that this antithrombotic property was mediated by inhibition of the synthesis of platelet thromboxane A2 (TXA2), a potent platelet aggregator and vasoconstrictor.

Drawing on these anti-platelet effects, in 1978 Dr Bob Goodlin and colleagues were the first to report the use of aspirin to prevent preeclampsia.They treated a thrombocytopenic patient with a history of recurrent early–onset severe preeclampsia using high doses of aspirin starting at 15 weeks, and reported that she delivered a live-born, although growth-restricted, infant at 34 weeks gestation. Eleven years later, Schiff and colleagues conducted the first randomized, placebo-controlled clinical trial of low-dose aspirin for the prevention of preeclampsia in high-risk women.

The American College of Obstetricians and Gynecologists recommends initiating use of low-dose aspirin (60 to 80 mg/d) during the late first trimester to prevent preeclampsia in women with a medical history of early-onset preeclampsia and preterm delivery (preeclampsia in more than 1 previous pregnancy¹.

The World Health Organization recommends the use of low-dose aspirin (75 mg/d) starting as early as 12 to 20 weeks of gestation for high-risk women (i.e., those with a history of preeclampsia, diabetes, chronic hypertension, renal or autoimmune disease, or multifetal pregnancies). It states that there is limited evidence regarding the benefits of low-dose aspirin in other subgroups of high-risk women².

The National Institute for Health and Clinical Excellence recommends that women at high risk for preeclampsia (i.e., women with a history of hypertension in a previous pregnancy, chronic kidney disease, autoimmune disease, type 1 or 2 diabetes, or chronic hypertension) take 75 mg/d of aspirin from 12 weeks until delivery. It recommends the same for women with more than 1 moderate-risk factor (first pregnancy, age ≥40 years, pregnancy interval >10 years, body mass index ≥35 kg/m², family history of preeclampsia, or multifetal pregnancies)³.

The American Heart Association and the American Stroke Association recommend that women with chronic primary or secondary hypertension or previous pregnancy-related hypertension take low-dose aspirin from 12 weeks until delivery⁴.

The American Academy of Family Physicians recommends low-dose aspirin (81 mg/d) after 12 weeks of gestation in women who are at high risk for preeclampsia⁵