Low-dose Aspirin Starting Before but Not After 16 Weeks Gestation May Reduce Preeclampsia

DynaMed Weekly Update - Volume 5, Issue 35

Low-dose aspirin has been associated with reduced incidence of hypertensive disorders in pregnant women (Cochrane Library 2007 Issue 2:CD004659) and is recommended for women with increased risk of preeclampsia (J Obstet Gynaecol Can 2008 Mar;30[3 Suppl 1]:S1-48, PDF). A recent systematic review suggests that aspirin should be started at or before 16 weeks gestation to show this benefit. Aspirin (50-150 mg/day with or without dipyridamole) was compared to placebo or no treatment in 27 randomized trials with 11,348 women at risk of preeclampsia. Risk factors included nulliparity, history of preeclampsia or other hypertensive disorders, and abnormal uterine artery Doppler ultrasound. In an analysis of 9 trials with treatment starting at ? 16 weeks gestation, aspirin was associated with reduced incidence of preeclampsia (risk ratio 0.47, 95% CI 0.34-0.65) (level 2 [mid-level] evidence). The number needed to treat (NNT) was 9 (95% CI 6-25). Aspirin starting at or before 16 weeks was also associated with decreased incidence of intrauterine growth restriction (IUGR) (risk ratio 0.44, 95% CI 0.3-0.65, NNT 11, 95% CI 8-20) and decreased risk of preterm birth (RR 0.22, 95% CI 0.1-0.5). There were no significant differences in either preeclampsia or IUGR in analysis of trials beginning aspirin after 16 weeks gestational age (Obstet Gynecol 2010 Aug;116(2 Part 1):402).

For more information, see the Hypertensive disorders of pregnancy and Intrauterine growth restriction topics in DynaMed.