A study conducted at St Thomas' Hospital, London, among 283 women at high risk of pre-eclampsia - a condition marked by high blood pressure and protein in the urine - found that giving high doses of vitamins C and E in the second half of pregnancy cut the incidence of the disorder by three-quarters.
Lucilla Poston, co-ordinator of the study funded by the charity Tommy's Campaign and published in The Lancet medical journal, said: "We are very excited by the results of this trial and its implications.
"We hope that this study may lead to an effective treatment which will prevent the onset of this devastating illness and its consequences."
However, experts warned that the findings needed confirmation by bigger trials before being adopted widely.
Pre-eclampsia kills about seven women and 1,000 babies a year in Britain and is the commonest reason for admission to hospital during pregnancy. It is marked by the failure of the placenta to develop normally - hindering the growth of the baby - and the development of high blood pressure and kidney damage in the mother, which can lead to fits.
Early symptoms of high blood pressure, which affects one in 10 pregnant women, and protein in the urine may be a warning sign of the full-blown disease, eclampsia.
There is no way of preventing or predicting the condition, but it can be detected by regular checks of blood pressure and urine. The only treatment is delivery of the baby, which may be put at risk because of its prematurity.
The cause of pre-eclampsia is not known. One candidate is high levels of free radicals - very reactive chemicals made from oxygen in the blood, which are known to play a role in the development of fatty arterial deposits that lead to heart disease.
Professor Poston and colleagues tested the idea that anti-oxidants to mop up the free radicals might help to prevent the condition. They chose women at high risk with a history of pre-eclampsia in pregnancy or signs of an abnormal blood flow to the placenta. Half were given supplements of 1 gram of vitamin C, a water-soluble anti-oxidant, and 400 units of vitamin E, which is fat soluble; the rest were given a placebo.
The results showed the incidence of pre-eclampsia was reduced by 76 per cent among those given the vitamins, compared with those given the placebo.
A statement on the study from Tommy's Campaign said the results "make it imperative that further investigation of the benefits of vitamin C and E supplementation in pregnancy is undertaken before they can be recommended for general use".
In a commentary in The Lancet, James Roberts, and Carl Hubel of the University of Pittsburgh, say the findings are encouraging but warn that there have been false dawns before over prevention of pre-eclampsia. Aspirin and calcium were found to be effective against the condition in small trials but their promise was not confirmed in larger trials.Reuse content