Glucose tolerance generally refers to a glucose tolerance test. Generally speaking, it is recommended to do the glucose tolerance test between 24 and 28 weeks of pregnancy. The glucose tolerance test usually involves fasting for 8 to 12 hours. Venous blood is taken early in the morning on an empty stomach to test fasting blood glucose and insulin, and venous blood is taken 30 minutes, 60 minutes, 120 minutes, and 180 minutes after 75g of oral glucose to measure blood glucose and insulin levels. The diagnostic criteria for gestational diabetes mellitus are: 75g oral glucose tolerance test at any time during pregnancy, 5.1mmol/L ≤ fasting blood glucose <7.0mmol/L, blood glucose ≥ 10.0mmol/L 1 hour after glycemic load, 8.5mmol/L ≤ 2 hours after glycemic load blood glucose <11.1mmol/L, any one of the above criteria, if one of these exceeds the other, then the diagnosis of gestational diabetes mellitus can be made. The diagnosis of gestational diabetes mellitus can be made if one of the above criteria is exceeded. During the glucose tolerance test, no eating, drinking, smoking, etc. are allowed. Pregnant women are advised to take the glucose tolerance test under the guidance of a physician for the sake of their own health and that of their fetus.