Vitamin D Supplementation for the Prevention of GDM

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. * Sign informed consent. - 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.