Prevention of pre-eclampsia by low-dose acetylsalicylic acid--a critical appraisal

Abstract

Pre-eclampsia has been shown to be associated with platelet activation and excessive release of vasoconstricting thromboxane preceding the onset of the disease. Low-dose acetylsalicylic acid (ASA) substantially inhibits thromboxane formation and may thus prevent pre-eclampsia from developing. In agreement with this hypothesis early randomised trials reported on promising reductions in pre-eclampsia risk and possible fetal growth retardation. Subsequent multicentre trials during the nineties failed to confirm a large benefit, which may in part be explained by late initiation of treatment, low dosages, low patient compliance and wide inclusion of women with concomitant disorders such as chronic hypertension, diabetes mellitus and kidney disease. A recent systematic review of all randomised trials showed an acceptable safety profile and a significant but only moderate reduction in the risk of pre-eclampsia regardless of gestation at trial entry or dose of ASA. There is now growing evidence that the earlier ASA treatment is started, the greater the reduction in the risk of pre-eclampsia is. Moreover, ASA has much stronger effects at higher (80 - 150 mg/day) than at lower doses in the protection against pre-eclampsia and the prevention of severe fetal growth retardation. No clinically important effects, however, have been found in patients with chronic hypertension, kidney disease or diabetes mellitus. In contrast, low dose ASA (100 mg/day) might benefit women with unfavourable obstetric history, in particular those with severe fetal growth retardation or pre-eclampsia with onset at < 32 weeks. The crucial time for starting treatment may be before 16 weeks and daily ingestion before bedtime appears useful. To start low-dose ASA at 20 - 24 weeks gestation seems only justified in women with abnormal uterine Doppler flow.