Vitamin C Levels in Pregnant Women and Efficacy of Vitamin C Supplements in the Prevention of Preterm Birth: A Systematic Review and Meta-Analysis

We aimed to conduct a systematic review and meta-analysis to investigate if there is a significant difference in vitamin C blood levels in women who had preterm birth compared to control group who did not and evaluate the efficacy of vitamin C supplements in preventing it. This manuscript presents a part of a larger systematic review and meta-analysis which was registered in PROSPERO (CRD42022371644). PubMed/MEDLINE, Scopus and Web of Science were searched up to February 15, 2024. Forward and backward citation searching was also performed. Studies were selected according to prespecified inclusion and exclusion criteria. Data were analyzed using Meta-Essentials: Workbooks for meta-analysis (Version 1.5). A total of 10 studies (11 reports) met all eligibility criteria: 5 studies (5 reports) assessing vitamin C levels and 5 studies (6 reports) assessing efficacy. No significant difference was found in vitamin C levels between women who had preterm birth and controls who had term delivery (Hedges' g=0.33; 95% confidence interval [CI]: −0.22, 0.88; p=0.091; I²=53.50%). Also, no differences were seen between women supplemented with vitamin C and controls taking placebo or having no vitamin C supplementation in the risk of preterm birth (risk ratio=0.94; 95% CI: 0.57, 1.55; p=0.730; I²=50.13%). Significant level of heterogeneity was observed in both meta-analyses, but results were robust in all sensitivity analyses. Our results suggest that there are no significant differences in vitamin C levels between women with preterm and term birth and that vitamin C supplementation doesn't influence the risk of preterm birth.