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Hypertension in pregnancy - Evidence
Evidence on the use of aspirin to prevent pre-eclampsia

There is good evidence from a Cochrane systematic review and a large meta-analysis that the use of low-dose aspirin results in a small reduction in the risk of developing pre-eclampsia in high risk women.

  • A Cochrane systematic review (search date: July 2006) assessed the effectiveness and safety of antiplatelet drugs in women at risk of pre-eclampsia [Duley et al, 2007]. Pre-eclampsia is associated with a reduction in the production of prostacyclin, which is a vasodilator, and excessive production of thromboxane, which is a vasoconstrictor and stimulant of platelet aggregation. It is hypothesised that low-dose aspirin in particular, might prevent or delay development of pre-eclampsia. Fifty-nine trials were included in the review (37,560 women).
    • Antiplatelet use was associated with:
      • A 17% reduction in the risk of pre-eclampsia (46 trials; 32,891 women; relative risk [RR] 0.83, 95% CI 0.77 to 0.89; NNT = 72).
      • A significantly better absolute risk reduction in women at high risk of pre-eclampsia (risk difference [RD] –5.2%, 95% CI –7.5 to –2.9; NNT = 19) compared with women at moderate risk (RD –0.84, 95% CI –1.37 to –0.3; NNT = 119).
      • An 8% reduction in the relative risk of pre-term birth (29 trials, 31,151 women; RR 0.92, 95% CI 0.88 to 0.97; NNT = 72).
      • A 14% reduction in fetal or neonatal deaths (40 trials, 33,098 women; RR 0.86, 95% CI 0.76 to 0.98; NNT = 243).
      • A 10% reduction in small-for-gestational-age babies (36 trials, 23,638 women; RR 0.90, 95% CI 0.83 to 0.98; NNT = 114).
      • A 40% reduction in the relative risk of pre-eclampsia in women with gestational hypertension (five trials, 1643 women; RR 0.60, 95% CI 0.45 to 0.78).
    • The authors concluded that antiplatelet drugs (low-dose aspirin in particular) have moderate benefits when used for prevention of pre-eclampsia and its consequences.
  • A meta-analysis of individual patient data from 31 randomized controlled trials, involving 32,217 women and their 32,819 infants, studied the primary prevention of pre-eclampsia using antiplatelet drugs [Askie et al, 2007]:
    • Women receiving antiplatelet drugs had a reduced risk of pre-eclampsia (RR 0.90, 95% CI 0.84 to 0.97).
    • There was no evidence that the effect of antiplatelet drugs was any different in a subgroup of women with chronic hypertension compared with women with other risk factors but no chronic hypertension.
    • The authors concluded that the use of antiplatelet agents during pregnancy results in moderate but consistent reductions in the relative risk of pre-eclampsia.

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