Daily doses of aspirin do not help prevent pre-eclampsia, concludes a major study.

This latest study of more than 9000 pregnant women contradicts earlier, far smaller, studies which concluded that low dose aspirin can reduce the incidence of pre-eclampsia by as much as three quarters.

Pre-eclampsia, a complication in the latter stages of pregnancy, leads to potentially fatal maternal high blood pressure and swelling.

The multi centred study by the group Collaborative Low dose Aspirin Study in Pregnancy (CLASP) found a reduction of only 12 per cent, "which was not significant".

Nor was there any evidence of a reduction in "intrauterine growth retardation" small babies in terms of their gestational age still birth or deaths before one month old.

The women in the study were randomly assigned to take either 60mg aspirin or a placebo, in order to supposedly prevent or treat pre-eclampsia or prevent or treat retarded growth.

The researchers suggest that earlier studies which claimed aspirin made a significant difference may have been biased particularly since all were very small. "It may be that some trials with unpromising results have not been published because they were less remarkable."

Far from being beneficial for many women, there is some evidence that taking aspirin during pregnancy may, in fact, be positively harmful, because it increases the risk of bleeding. Although the CLASP researchers found no significant increases in placental haemorrhages or in bleeding during preparation for epidural "there was a slight increase in use of blood transfusion after surgery," they said.

!ALancet, 12 March 1994.