| S/N | Nation | Treatment group | Sample size | Dosage/ Intervention | Treatment Duration | Timing of vitamin D intervention | Results | Reference |
| 1 | Europe | Vitamin D Placebo | 70 70 | 50,000 IU/2 weeks | 10 weeks | 14 - 16 | No association found between vitamin D supplementation and developing GDM. | [79] |
| 2 | Iran | Vitamin D Placebo | 46 45 | 5000 Units/week | Until the 26th week | First trimester | Incidence of GDM in intervention group was statistically lower than in control group (P < 0.001) | [53] |
| 3 | Iran | Vitamin D3 Placebo | 36 36 | 50,000 IU/2 weeks | 10 months | 24 - 28 weeks | Vitamin D supplements were associated with a significant decrease in fasting glucose (P = 0.01) and HbA1c (P = 0.02). | [54] |
| 4 | China | Calciferol Low dose Medium dose High dose Placebo |
38 38 37 20 | 200 IU/daily 2000 IU/daily 4000 IU/daily | Until the delivery 25 days 12.5 days | 24 - 28 weeks | High and medium doses of vitamin D supplementation reduces Insulin and HOMA‑IR levels in mothers with GDM (P < 0.01). | [55] |
| 5 | Australia | Vitamin D3 High dose Low dose Nonrandomized |
89 90 24 | 5000 IU/daily 400 IU/daily | Until the delivery (from <20 weeks) | <20 weeks | No association found between vitamin D supplementation and developing GDM. | [80] |
| 6 | Iran | Vitamin D3 Placebo | 27 27 | 50,000 IU twice (at baseline & day 21) | 6 weeks | 24 - 28 weeks | Vitamin D supplementation significantly decreases concentrations of FPG (P < 0.001), serum insulin (P = 0.01) & HOMA-IR (P < 0.001). | [56] |
| 7 | China | Plain yogurt with vitamin D3 Plain yogurt without vitamin D3 | 52
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| Two servings (200 g) of supplemented yogurt per day (500 IU vitamin D3 per serving) | 16 weeks | 13 weeks | Vitamin D supplements statistically reduce FPG (P = 0.04), serum insulin (0.03) & HOMA-IR (P = 0.01). | [57] |