Gestational diabetes mellitus (GDM) has been recognized as a significant risk factor for unfavorable pregnancy outcomes. Prevalence of
vitamin D deficiency is highly prevalent among women with GDM. This study was designed to assess the effect of
vitamin D supplementation on pregnancy outcomes of pregnant women with GDM who were not on oral
hypoglycemic agents. This randomized controlled clinical trial was performed among 45 pregnant women diagnosed with GDM at 24-28 weeks' gestation. Subjects were randomly assigned to consume either
vitamin D supplements (
cholecalciferol) or placebo. Individuals in the
vitamin D group (n=22) received 50 000 IU
vitamin D3 pearl 2 times during the study: at study baseline and day 21 of intervention and those in placebo group (n=23) received 2
placebos at the mentioned times. Fasting blood samples were taken at baseline to measure fasting plasma
glucose. Participants underwent a 3-h oral
glucose tolerance tests (OGTT) and the blood samples were collected at time 60, 120, and 180 min to measure plasma
glucose levels. Newborn's weight, height, head circumference, Apgar score, and
hyperbilirubinemia were determined. Taking
vitamin D supplements, compared with placebo, resulted in improved pregnancy outcomes; such that those in the
vitamin D group had no case of
polyhydramnios, while 17.4% of subjects in placebo group had this condition (p=0.04). In addition, newborn's
hyperbilirubinemia was significantly lower in
vitamin D group than that in placebo group (27.3% vs. 60.9%, p=0.02). In conclusion,
vitamin D supplementation for 6 weeks among pregnant women with GDM resulted in decreased maternal
polyhydramnios and infant
hyperbilirubinemia compared with placebo. Clinical trial registration number www.irct.ir:IRCT201305115623N7.