Vitamin B 12 and gestational diabetes mellitus: a systematic review and meta-analysis.

The relationship between vitamin B 12 and gestational diabetes mellitus (GDM) remains controversial. To comprehensively evaluate the relationship between vitamin B 12 and GDM, and to provide more information on GDM prevention, this study provides a systematic review and meta-analysis of vitamin B 12 and GDM. As of September 22, 2021, 304 articles were searched in PubMed, Web of Science, EMBASE, and Cochrane databases, of which 15 studies met the inclusion criteria. Results presented there was no association between maternal vitamin B 12 concentration during the first trimester with GDM, however, low vitamin B 12 concentration in the second or third trimester of pregnancy was related to an increased risk of GDM. Compared with the non-GDM group, the vitamin B 12 concentration in the GDM group was remarkably decreased (MD: -10·79; 95%CI: -21·37, -0·21), and vitamin B 12 deficiency increased the risk for GDM (OR: 1·59; 95%CI: 1·10, 2·29). These effects were more significant among Asians. In addition, an increased ratio of high folate to low vitamin B 12 in serum also increased the risk of GDM (OR: 1·87; 95% CI: 1·46, 2·41). These results suggest that more vitamin B 12 may need to be provided during pregnancy.