Vitamin C supplementation in pregnancy

BACKGROUND: Vitamin C supplementation may help reduce the risk of pregnancy complications like pre-eclampsia, intrauterine growth restriction and maternal anaemia. There is a need to evaluate the efficacy and safety of vitamin C supplementation in pregnancy. OBJECTIVES: To evaluate the effects of vitamin C supplementation, alone or in combination with other separate supplements on pregnancy outcomes, adverse events, side-effects and use of health resources. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (23 June 2004), Cochrane Central Register of Controlled Trials (The Cochrane Library 2004, Issue 2), MEDLINE (1966 to May 2004), Current Contents (1998 to May 2004) and EMBASE (1980 to May 2004). We updated the search of the Cochrane Pregnancy and Childbirth Group's Trials Register on 7 May 2010 and added the results to the awaiting classification section. SELECTION CRITERIA: All randomised or quasi-randomised controlled trials evaluating vitamin C supplementation in pregnant women. Interventions using a multivitamin supplement containing vitamin C or where the primary supplement was iron were excluded. DATA COLLECTION AND ANALYSIS: Two authors independently assessed trials for inclusion, extracted data and assessed trial quality. MAIN RESULTS: Five trials involving 766 women are included in this review. No difference was seen between women supplemented with vitamin C alone or in combination with other supplements compared with placebo for the risk of stillbirth (relative risk (RR) 0.87, 95% confidence intervals (CI) 0.41 to 1.87, three trials, 539 women), perinatal death (RR 1.16, 95% CI 0.61 to 2.18, two trials, 238 women), birthweight (weighted mean difference (WMD) -139.00 g, 95% CI -517.68 to 239.68, one trial, 100 women) or intrauterine growth restriction (RR 0.72, 95% CI 0.49 to 1.04, two trials, 383 women). Women supplemented with vitamin C compared with placebo were at increased risk of giving birth preterm (RR 1.38, 95% CI 1.04 to 1.82, three trials, 583 women). Significant heterogeneity was found for neonatal death and pre-eclampsia. No difference was seen between women supplemented with vitamin C compared with placebo for the risk of neonatal death (RR 1.73, 95% CI 0.25 to 12.12, two trials, 221 women), using a random-effects model. For pre-eclampsia, women supplemented with vitamin C were at decreased risk when using a fixed-effect model (RR 0.47, 95% CI 0.30 to 0.75, four trials, 710 women), however this difference could not be demonstratedwhen using a random-effects model (RR 0.52, 95% CI 0.23 to 1.20, four trials, 710 women). AUTHORS' CONCLUSIONS: 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.]