It's official: low dose aspirin won't do pregnant mothers any good if they are suffering from high blood pressure or their baby's growth is retarded.

An analysis of several controlled trials of over a thousand women has overturned the conventional wisdom that aspirin could control pregnancy induced hypertension and so treat pre eclampsia and fetal growth retardation.

This theory derived from a 1985 French study which reported a significant decrease in protein in the urine (a risk marker for eclampsia) and perinatal death when low doses of aspirin were given to women at risk of hypertension. Seven equally small trials appeared to report better outcomes among aspirin users than among non users, giving a virtual green light to aspirin use during pregnancy.

However, this latest Italian trial, which is larger than all the previous ones put together, failed to find any benefit whatsoever from aspirin.

An accompanying editorial in The Lancet said the discrepancy could be due to the fact that the results in the early small trials were biased or concerned women at high risk. "Apart from women with cirulating lupus anticoagulant, there is no identifiable group of pregnancies guaranteed to receive more benefit than harm from low dose aspirin," it concludes.