A randomised, double-blind placebo-controlled trial of ascorbic acid supplementation for the prevention of preterm labour. Effect of antioxidants on the occurrence of pre-eclampsia in women at increased risk: a randomised trial. Antioxidants in the treatment of severe pre-eclampsia: an explanatory randomised controlled trial.
In a previous study from this institution, patients at high risk for preterm labour were screened for the presence of bacterial vaginosis (BV). When BV was present, they were randomised to receive either treatment (metronidazole) or placebo (vitamin C). There were significantly more patients with preterm labour in the metronidazole group. The aim of this double-blind randomised placebo-controlled trial study was to determine whether vitamin C could indeed reduce the recurrence risk of preterm labour. Patients with a history of preterm labour in a preceding pregnancy were randomised to receive 250 mg vitamin C or a matching placebo twice daily until 34 weeks' gestation. They attended a dedicated premature labour clinic. Significantly more women delivered before term in the group that received vitamin C, but there was no difference in the outcome of the babies between the two groups. Supplementation with vitamin C did not prevent premature labour. Oxidative stress has been implicated in the pathophysiology of pre-eclampsia. This randomised controlled trial investigated the effect of supplementation with vitamins C and E in women at increased risk of the disorder on plasma markers of vascular endothelial activation and placental insufficiency and the occurrence of pre-eclampsia.
                283 women were identified as being at increased risk of pre-eclampsia by abnormal two-stage uterine-artery doppler analysis or a previous history of the disorder and were randomly assigned vitamin C (1000 mg/day) and vitamin E (400 IU/day) or placebo at 16-22 weeks' gestation. Plasma markers of endothelial activation (plasminogen-activator inhibitor 1 [PAI-1]) and placental dysfunction (PAI-2) were measured every month until delivery. Pre-eclampsia was assessed by the development of proteinuric hypertension. Analyses were done by intention to treat, and in the cohort who completed the study.
                Supplementation with vitamins C and E was associated with a 21% decrease in the PAI-1/PAI-2 ratio during gestation (95% CI 4-35, p=0.015). In the intention-to-treat cohort, pre-eclampsia occurred in 24 (17%) of 142 women in the placebo group and 11 (8%) of 141 in the vitamin group (adjusted odds ratio 0.39 [0.17-0.90], p=0.02). In the cohort who completed the study (81 placebo group, 79 vitamin group), the odds ratio for pre-eclampsia was 0.24 (0.08-0.70, p=0.002).
                Supplementation with vitamins C and E may be beneficial in the prevention of pre-eclampsia in women at increased risk of the disease. Multicentre trials are needed to show whether vitamin supplementation affects the occurrence of pre-eclampsia in low-risk women and to confirm our results in larger groups of high-risk women from different populations. To determine whether antioxidant therapy alters the disease process in severe early onset pre-eclampsia, in support of the hypothesis that increased lipid peroxides and reactive oxygen species production-play an important role in the pathogenesis of the disease.
                Randomised, double-blind, placebo controlled trial.
                Two tertiary care, referral hospitals in Johannesburg, South Africa.
                Women with severe pre-eclampsia diagnosed between 24 and 32 weeks of gestation.
                Combined antioxidant treatment with vitamin E (800 IU/day), vitamin C (1000 mg/day), and allopurinol (200 mg/day).
                Primary outcomes: 1. prolongation of pregnancy and 2, biochemical assessment of lipid peroxides and antioxidants. Secondary outcomes: data on maternal complications, side effects of treatment, infant outcomes and regular assessment of haematologic and renal parameters.
                The proportion of women delivered within 14 days in the antioxidant group was 52% (14/27) compared with 76% (22/29) in the placebo group (relative risk 0.68, 95% confidence interval 0.45-1.04). One woman in each group had eclampsia. Eleven women (42%) in the antioxidant and 16 (59%) in the placebo group required two antihypertensives for blood pressure control. Trial medications were well tolerated with few side effects. Lipid peroxide levels were not significantly altered in the antioxidant and placebo groups. Serum uric acid levels decreased and vitamin E levels increased significantly.
                The results of this explanatory randomised trial do not encourage the routine use of antioxidants against pre-eclampsia. However, further research with modified strategies such as earlier initiation of therapy or different combinations seem worthwhile.
The data are too few to say if vitamin C supplementation either alone or in combination with other supplements is beneficial during pregnancy. Preterm birth may have been increased with vitamin C supplementation.
[Note: The 32 citations in the awaiting classification section of the review may alter the conclusions of the review once assessed.]