This study was a double-blind multicenter randomized controlled study.

This study intends to adopt a randomized controlled study design, and randomly divide pregnant women at high risk of GDM into intervention group (VitD3:1600 IU/ day) (n=800) and control group (placebo:2 tablets/day) (n=800) until the end of delivery. The risk of GDM in pregnant women of the two groups was compared, the preventive effect of high-dose VitD supplementation during pregnancy on different subtypes of GDM was determined, and the effects of VitD supplementation on VitD nutritional status during pregnancy and birth outcome and health of offspring were explored, so as to provide evidence-based basis for rational VitD supplementation during pregnancy.

Inclusion Criteria:

• Pregnant women who are 8 to 14 weeks pregnant ; ② 18 to 45 years old; ③ Pregnant women at high risk of GDM (meeting any of the following conditions) : A) BMI ≥24 kg/m2 before or during pregnancy; B) family history of diabetes or GDM; C) Previous pregnancy diagnosed as GDM; D) with a history of macrosomia (≥4000 g); E) A history of abnormal glucose tolerance: 5.7-6.4% hBA1c or 6.1-7.0 mmol/L fasting blood glucose.

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Exclusion Criteria:

• Patients with a history of diabetes or currently diagnosed diabetes (including type 1 and type 2 diabetes);

  • HBA1c ≥6.5% or fasting blood glucose & GT;7.0 mmol/L with obvious symptoms of diabetes;

    • Patients with current or past abnormalities in calcium metabolism (hypoparathyroidism/hyperthyroidism, kidney stones), high urinary calcium or hypercalcemia;

      • Daily VitD intake & GT;800 IU. ⑤ Suffering from serious chronic diseases (heart, lung, liver, kidney and other dysfunction) or mental illness;

        • They cannot walk 100 meters safely; 7. Multiple pregnancies or assisted reproduction; ⑧ need complex diet;

          • Cannot speak Mandarin fluently; ⑩ Those who are participating in other clinical trials or who are considered unsuitable for clinical trials by researchers for other reasons.

This study only applied to women with normal pregnancies