The aim of a new study published in the BJOG was to evaluate the relationship between vitamin D (VD) level and gestational diabetes mellitus (GDM). Here, a data search was performed from EMBASE, MEDLINE, Cochrane library, and China Biology Medicine disc, through May 2017. This study included 87 observational studies on the relationship between VD and GDM, free from Hawthorne effect, and 25 randomized controlled trials of VD supplementation during pregnancy for preventing or treating GDM. The results revealed that low blood VD level during pregnancy was associated with a higher risk of GDM. While, blood VD level for subjects with GDM were lower than that of controls. Additionally, blood VD level was associated with fasting plasma glucose (FPG) and homeostatic model assessment-insulin resistance (HOMA-IR). It was noted that VD intervention during pregnancy could change blood level of VD, fasting serum insulin (FINS), FPG, HOMA-IR, glutathione, C-reactive protein, and lipid. Hence, it was inferred that low blood VD level could increase the risk of GDM, and VD supplementation during pregnancy could ameliorate the condition of GDM.