A Cochrane Review5 updated in 2007 demonstrated that low-dose aspirin provided a moderate (19%) reduction in the overall risk of developing preeclampsia. New stratified analysis of the data indicates that in moderate-risk women, antiplatelet therapy is associated with a 15% reduction, and that high-risk women have a 27% reduction in the risk of developing preeclampsia. The effect on small-for-gestational-age infants revealed no overall clinically significant differences.
Aspirin dosing: One study recommends >75 mg/day
Studies varied in the aspirin dosage they used and duration of treatment. In all RCTs, the dose of aspirin ranged from 50 mg/day to 150 mg/day. Earlier trials used lower doses of aspirin (50–75 mg/day), while recent trials used 100 mg or more per day.
Early RCTs revealed no correlation between the dose of aspirin and the prevention of preeclampsia. However, Villar et al6 showed a greater effect among women treated with doses greater than 75 mg/day of aspirin (RR=0.49; 95% CI, 0.38–0.63).6
No evidence of harm from aspirin
There is no evidence of harm from low-dose aspirin therapy—including placental abruption, antenatal admissions, fetal intraventricular hemorrhage and other neonatal bleeding complications, admission to neonatal care unit, induction of labor, or caesarean delivery—regardless of initial risk stratification.7
Recommendations from others
The 2002 American College of Obstetricians and Gynecologists Practice Bulletin states that low-dose aspirin in women at low risk has not been shown to prevent preeclampsia and therefore is not recommended. They make no specific statement regarding the use of low-dose aspirin in moderate- to high-risk pregnancies.8
The Australasian Society for the Study of Hypertension in Pregnancy conclude that low-dose aspirin for prevention of preeclampsia is reasonable for the following conditions: 1) prior fetal loss after first trimester due to placental insufficiency or severe fetal growth retardation, and 2) women with severe early onset preeclampsia in previous pregnancy necessitating delivery ≤32 weeks gestation. Despite difficulties in predicting who will deliver preterm, consider women who have had severe early-onset preeclampsia in a previous pregnancy for low-dose aspirin therapy.9
The Canadian Hypertension Society Consensus Panel concludes low-dose aspirin therapy is effective in decreasing the incidence of preterm delivery and early-onset preeclampsia among women at risk of developing the syndrome.10