But the British scientists who conducted the study warned that pregnant women should not rush out and start taking large doses of the vitamins since their findings are preliminary they haven't even yet determined if those high doses are safe for the developing fetus.
The benefit suggested by the study, the first to investigate the vitamins' potential to prevent pre-eclampsia, must be confirmed in large-scale experiments, said the lead researcher, Lucilla Poston, a professor who runs the fetal health research group at Guy's, King's and St. Thomas' School of Medicine in London.
Pre-eclampsia, which occurs in about 5 percent of pregnancies, is a potentially fatal condition in which blood vessels throughout the body and womb constrict, reducing the amount of the mother's blood that reaches the fetus.
It develops late in pregnancy and produces a sudden rise in blood pressure and swelling. If untreated, it can progress to convulsions, bleeding in the mother's brain, liver or kidney, and force early delivery to save the mother and child.
Women at higher risk for the complication include old or very young mothers, those in their first pregnancy, those carrying twins and women who are overweight, have diabetes, high blood-pressure or blood-clotting disorders.
Scientists believe pre-eclampsia could be connected to the damage that oxygen does to the blood vessels and to impaired activity of antioxidants, substances that fight the attacks of oxygen.
Poston's study of 160 pregnant women at high risk for the condition, published in this week's issue of The Lancet, a British medical journal, found that taking 1,000 milligrams of vitamin C and 400 International Units of vitamin E daily cut the chances of pre-eclampsia by 76 percent.
Such high doses are fairly common in some supplements, but they are many times higher than the recommended intake for pregnant women.
Six of the 79 women taking the vitamins, or 8 percent, developed the condition, but 21 of the 81 taking the fake tablets, or 26 percent, experienced the complication.
"This finding is both encouraging and frightening," James Roberts, a professor at the University of Pittsburgh unconnected with the study, wrote in a critique for The Lancet.
He cited the apparent promise of aspirin and calcium supplements, which seemed to work in small early studies, but proved unsuccessful when investigated further.
Studies have shown that women with pre-eclampsia have lower levels of antioxidants such as vitamins C and E in their blood.
Research also has indicated that women who already have pre-eclampsia and are given vitamin C and E supplements to boost their antioxidant activity suffer less oxygen damage to their placenta than those not given the vitamins.
Poston found a similar impovement in an indicator for antioxidant activity in her study, which supports the theory that oxygen damage is at least partly responsible for pre-eclampsia. But scientists don't know what effect the vitamins would have on pregnant women who are unlikely to experience the complication anyway, she said.