Dietary supplements could prevent a dangerous complication of pregnancy, research has suggested. Up to one in ten pregnancies is affected by pre-eclampsia, with symptoms including high blood pressure, headaches, blurred vision and swelling. The exact cause is unknown, but it is thought to be linked to problems with blood vessels in the placenta. In the latest study, published in the British Medical Journal, experts assessed the impact on the risk of pre-eclampsia of a supplement containing an amino acid and antioxidant vitamins.