IRCT201305115623N7 IRCT 2013-05-23 Kashan University of Medical Sciences Effect of vitamin D in treatment of gestational diabetes Effect of vitamin D supplementation on insulin resistance and inflammatory factors in women with gestational diabetes 2013-05-15 anticipated 54 Complete https://irct.ir/trial/6037 interventional Randomization: Randomized, Blinding: Double blinded, Placebo: Used, Assignment: Parallel, Purpose: Treatment, Randomization description: To decrease potential confounding effects, all participants will have stratified randomization according to BMI and weeks of gestation. Then, participants in each block will be randomly allocated into two treatment groups to take either vitamin D supplement or placebo. Randomization will be done by the use of Stat Trek software. Participants, investigators or the assessors of the outcomes are also unaware of the study groups. https://stattrek.com/statistics/random-number-generator.aspx, Blinding description: Randomization and allocation will be concealed from the researchers and participants until the final analyses are completed. Another person at the maternity clinics affiliated with Kashan University of Medical Sciences, who is not involved in the trial and not aware of random sequences, will be assigned the participants to the numbered bottles of capsules. Supplements and placebo are in the same packaging at the Barij Essence pharmaceutical company. Only the code is written on the packages. Patients and researcher do not know the type of drug and after analyzing the data, packet codes are decoded. 2 Gestational diabetes mellitus. Intervention 1: Intervention group: Vitamin D3 capsule ( Zahravi Pharm Co, Iran), 50000 IU, every 3 weeks for 6 weeks orally. Intervention 2: Control group: Placebo capsule (Barij Essence Co, Iran), every 3 weeks for 6 weeks orally. Undecided - It is not yet known if there will be a plan to make this available Justification or reason for indecision in sharing IPD is Undecided - It is not yet known if there will be a plan to make this available