The Hyperglycemia and Adverse Pregnancy Outcomes Study investigated blood glucose and pregnancy outcomes in more than 25,000 pregnant women at 24 to 32 weeks of gestation and confirmed that elevated blood glucose has an adverse effect on maternal and infant pregnancy outcomes, and that this effect increases continuously with elevated blood glucose. The negative effects persisted even when blood glucose was mildly elevated and did not reach levels previously considered abnormal. The results of the HAPO study have led to a consideration of the diagnostic criteria for gestational diabetes mellitus. Screening and diagnostic criteria for GDM: ①In individuals with risk factors for diabetes, undiagnosed T2DM is screened for at the first prenatal visit according to the diagnostic criteria for diabetes; ②For pregnant women with undiagnosed diabetes, GDM can be screened for at 24-28 weeks of gestation using the 75 g oralglucose tolerance rest (OGTT). The diagnostic cut points are: fasting blood glucose ≥ 5.1 mmol/L or 1-hour blood glucose ≥ 10.0 mmol/L or 2-hour blood glucose ≥ 8.5 mmol/L, meeting any point of blood glucose value can diagnose GDM; ③Women with GDM should be screened for diabetes at 6 to 12 weeks postpartum to determine whether diabetes is permanently present; ④Women with a history of GDM should be screened for diabetes at least every 3 years to determine whether diabetes or prediabetes has developed. Compared to the previous diagnostic criteria, the new criteria have a number of differences: (1) Pregnant women with risk factors for diabetes will be screened and diagnosed at the time of their initial delivery according to the prevailing diagnostic criteria; (2) The recommendation that pregnant women without risk factors for diabetes do not need to be screened for GDM has been eliminated; (3) The glycemic cut point for diagnosis has changed and abnormally elevated blood glucose at any point is required for diagnosis; and (4) The most significant change is the selection of 75 weeks for screening of women with diabetes. The most significant change is the selection of 75 g OGTT as the diagnostic method and the discontinuation of the use of 100 g OGTT.