Therefore, this study aimed to determine the effect of vitamin D supplementation on fasting blood glucose (FBG) levels, fasting blood insulin (FBI) levels and insulin resistance index (HOMA-IR) (primary outcomes) and symptoms of depression, musculoskeletal pain, frequency of gestational diabetes and the frequency of abortion (secondary outcomes) in pregnant women with a gestational age of 8–10 weeks. This evidence concerns the gene INS and gestational diabetes.