Rates of pre eclampsia in women with type 1 diabetes are two to four times higher than in normal pregnancies. Diabetes is associated with antioxidant depletion and increased free radical production, and an increasing body of evidence suggests that oxidative stress and endothelial cell activation may be relevant to disease pathogenesis in pre eclampsia. The Diabetes and Pre eclampsia Intervention Trial (DAPIT) aims to establish if pregnant women with type 1 diabetes supplemented with vitamins C and E have lower rates of pre eclampsia and endothelial activation compared with placebo treatment. Methods: DAPIT is a randomised multicentre double blind placebo controlled trial that will recruit 756 pregnant women with type 1 diabetes from 20 metabolic antenatal clinics in the UK over 4 years. Women are randomised to daily vitamin C (1000 mg) and vitamin E (400 IU) or placebo at 8- 2 weeks of gestation until delivery. Maternal venous blood is obtained at randomisation, 26 and 34 weeks, for markers of endothelial activation and oxidative stress and to assess glycaemic control. The primary outcome of DAPIT is pre eclampsia. Secondary outcomes include endothelial activation (PAI- 1/PAI- 2) and birthweight centile. Rates of pre eclampsia in women with type 1 diabetes are two to four times higher than in normal pregnancies. Diabetes is associated with antioxidant depletion and increased free radical production, and an increasing body of evidence suggesting that oxidative stress and endothelial cell activation may be relevant to disease pathogenesis in pre eclampsia. The Diabetes and Pre eclampsia Intervention Trial (DAPIT) aims to establish if pregnant women with type 1 diabetes supplemented with vitamins C and E have lower rates of pre eclampsia and endothelial activation compared with placebo treatment. Methods: DAPIT is a randomized multicentre double blind placebo controlled trial that will recruit 756 pregnant women with type 1 diabetes from 20 metabolic antenatal clinics in the UK over 4 years. Women are randomized to daily vitamin C (1000 mg) and vitamin E (400 IU) or placebo at 8- 2 weeks of gestation until delivery. Maternal venous blood is obtained at randomization, 26 and 34 weeks, for markers of endothelial activation and oxidative stress and to assess glycaemic control. The primary outcome of DAPIT is pre eclampsia. Secondary outcomes include endothelial activation (PAI-1 / PAI-2) and birthweight centile.