(BJOG. 2016;123:588–597) Women who are overweight or obese during pregnancy have an increased risk of gestational diabetes, pregnancy-induced hypertension, pre-eclampsia, and cesarean section, and have a longer hospital stay.

Background: The difference in serum 25-hydroxyvitamin D3 (25-(OH) D3) level between the gestational diabetes mellitus (GDM) and healthy pregnant women was analyzed, to provide the experimental evidence for the vitamin supplement in pregnant women, especially those with GDM. Methods: Pregnant women (n=50) who received prenatal care in the Obstetrical Clinic of Xuzhou Maternity and Child Health Care Hospital in summer and winter of 2016 were enrolled. They were assigned to the summer GDM group, winter GDM group, summer control group and winter control group. The level of serum 25- (OH)D3 was determined using immunochromatography. Results: The mean level of serum 25-(OH)D3 in pregnant women of four groups was lower than normal level. Compared with control group in corresponding season, the winter and summer GDM groups had significantly lower level of 25-(OH)D3 than the winter and summer control groups (P<0.05). The winter GDM group had significantly lower level of 25-(OH)D3 than the summer GDM group (P<0.05). The winter control group had significantly lower level of 25-(OH)D3 than the summer control group (P<0.05). The percentage of deficient 25-(OH)D3 level was the highest in winter GDM group. Vitamin D deficiency was severer in pregnant women with GDM than healthy pregnant women. In winter, vitamin D deficiency was severer than that in summer. Conclusion: Pregnant women, especially those with GDM, should pay more attention to vitamin D supplementation.