The diagnostic criteria for gestational diabetes involve a pregnant woman undergoing a 75-gram glucose test at any time during pregnancy to measure fasting blood glucose, blood glucose one hour after consuming glucose, and blood glucose two hours after consuming glucose. The thresholds are: fasting blood glucose equal to or greater than 5.1 mmol/L, blood glucose one hour after glucose intake equal to or greater than 10.0 mmol/L, and blood glucose two hours after glucose intake equal to or greater than 8.5 mmol/L. Diagnosis of gestational diabetes can be made if blood glucose levels exceed these standards at any of the three time points. In China, pregnant women typically undergo the 75-gram glucose test between the 24th to 28th week of pregnancy. Women at high risk for gestational diabetes are advised to undergo the 75-gram glucose test early.