Abstract

Introduction: Gestational diabetes mellitus (GDM) is a pregnancy complication characterized by intolerance to carbohydrates and metabolic diseases. Vitamin D supplement prescription has been shown to be effective on glycemic control and other pregnancy outcomes. Therefore, this study aimed to investigate the effect of high dose of vitamin D supplement on glycemic control in pregnancy and its effect on reducing other adverse outcomes of pregnancy. Methods: The study was conducted on 40 pregnant women in the first trimester who had impaired glucose tolerance test by the randomized clinical trial method. Subjects were divided into two groups. Simultaneously with the regimen, the intervention group was given a higher dose of vitamin D and the control group received vitamin D routinely. Then, HbA1c level, fasting blood sugar, fasting serum insulin, and insulin resistance were measured at the beginning and 6 weeks later. Patients were followed up for pregnancy complications until the end of pregnancy. Results: Fasting blood sugar, HbA1C, serum insulin level, and HOMA-IR level after receiving vitamin D in the case group were less than the control group, which were significantly different (p.v <0.001). Cases that required insulin therapy and preterm labor were higher in the control group, but it was not significant. There were no significant differences in other outcomes of pregnancy. The level of vitamin D in umbilical cord blood was higher and significant in the case group (p.v <0.001) but there was no significant difference with pregnancy complications in the two groups. Conclusion: Our study showed that administering a dose higher than the current vitamin D recommendation in pregnancy can help prevent gestational diabetes and its adverse outcomes.