OBJECTIVE: To assess the evidence available on the use of vitamin C supplementation greater than recommended dietary intake to reduce preterm birth rates. STUDY DESIGN: Systematic review of randomized controlled trials using vitamin C alone or with one other supplement other than iron. Trials must report preterm birth rates but can have other primary outcomes. Preterm birth is defined as birth at less than 37 weeks' gestational age for this review. Review focused on studies with populations representative of Organization for Economic Co-operation and Development countries. RESULTS: Inadequate level of evidence on the use of vitamin C alone to prevent preterm birth rates in low-risk populations based on one study. Three studies provided convincing evidence of no benefit in low-risk groups of use of vitamins C and E combined. Three studies provided adequate evidence of no benefit in high-risk groups of use of vitamins C and E combined. CONCLUSION: The available evidence supports no benefit gained from using vitamin C to prevent preterm birth. Evidence does not support limiting use of vitamin C supplementation for other indications.