According to the 2014 Guidelines for the Diagnosis and Treatment of Gestational Diabetes Mellitus: Any one of the three 75g OGTT results reaching or exceeding the standard can diagnose GDM.

1. It is recommended that medical institutions perform OGTT on all pregnant women who have not been diagnosed with PGDM or GDM at 24-28 weeks of gestation and at the first visit after 28 weeks. Fast for at least 8 hours before OGTT, maintain a normal diet for 3 consecutive days before the test, with a daily intake of at least 150g of carbohydrates, sit still, and refrain from smoking during the test. During the test, drink 300ml of liquid containing 75g of glucose within 5 minutes, and draw venous blood from the pregnant woman before and 1 and 2 hours after drinking the glucose solution (time calculated from the start of drinking the glucose solution), put it in a tube containing sodium fluoride, and measure blood glucose levels using the glucose oxidase method.

2. For pregnant women with high-risk factors for GDM or in areas with limited medical resources, it is recommended to first check FPG at 24-28 weeks of gestation. If FPG ≥ 5.1 mmol/L, GDM can be diagnosed directly without OGTT; if FPG < 4.4 mmol/L (80 mg/dL), the possibility of GDM is very low, and OGTT can be temporarily omitted. If FPG ≥ 4.4 mmol/L and < 5.1 mmol/L, OGTT should be performed as soon as possible.

3. For pregnant women with high-risk factors for GDM, if the first OGTT result is normal, OGTT can be repeated in late pregnancy if necessary.

4. FPG levels gradually decrease with gestational weeks in early and mid-pregnancy, especially in early pregnancy, so FPG levels in early pregnancy cannot be used as a diagnostic basis for GDM.

5. For those who have not been regularly checked, if the first visit is after 28 weeks of gestation, it is recommended to perform OGTT or FPG test at the first visit or as soon as possible after the visit.