Background: Although several studies have investigated the association between maternal serum vitamin D levels and risk of pre-eclampsia, findings are inconsistent. This systematic review and meta-analysis of published observational studies was conducted to summarize the evidence on the association between maternal serum vitamin D levels and risk of pre-eclampsia.
Methods: PubMed, ISI (Web of science), SCOPUS, SCIRUS, Google Scholar, and EMBASE databases were searched to identify related articles published through December 2012. For systematic review, we found 15 articles that assessed the association between maternal serum vitamin D levels and risk of pre-eclampsia. The meta-analysis was done on 8 studies that reported odds ratios or relative risks for pre-eclampsia. Between-study heterogeneity was examined using Cochran's Q test and I(2). Subgroup analysis and meta-regression were used to find possible sources of heterogeneity.
Results: The meta-analysis on 8 relevant papers revealed an overall significant association between vitamin D deficiency and risk of pre-eclampsia; however, there was significant between-study heterogeneity (I(2) = 52.7%; P = .039). In the subgroup analysis, we found that the overall effect was significant for studies that defined vitamin D deficiency as 25(OH)D ≤ 50 nmol/L (20 ng/mL), but not for those that considered it as <38 nmol/L (15.2 ng/mL). The association was seen for "cohort or nested case-control studies" as well as for "cross-sectional or case-control studies" (2.78; 1.45-5.33; P = .002). When the analysis was done by study location, the associations remained significant only for studies that came from the United States.
Conclusion: There was a significant relationship between vitamin D deficiency and increased risk of pre-eclampsia. Further studies are required, particularly in developing countries.