Glucose tolerance is an important maternity test during pregnancy, and the best time to test is at 24-28 weeks of pregnancy. As pregnancy progresses, the blood glucose level of pregnant women in the early and middle stages of pregnancy will gradually decrease, while the insulin sensitivity of pregnant women in the middle and late stages of pregnancy decreases, and at this time, if insulin secretion is insufficient, gestational diabetes is likely to occur. Therefore, at 24-28 weeks of pregnancy, all pregnant women should undergo a 75g glucose tolerance test. Pregnant women should have a normal diet 3 days before the glucose tolerance test, no more meals after 10:00 p.m. on the night before the test, and the test will be performed on the day of the test in a fasting and resting state. Gestational diabetes mellitus is diagnosed if the fasting blood glucose is >5.1mmol/L, 1 hour postprandial blood glucose is >10mmol/L, and 2 hours postprandial blood glucose is >8.5mmol/L, with any of these points reaching the standard. Pregnant women with high-risk factors may need to repeat the glucose tolerance test in late pregnancy if necessary, even though the first glucose tolerance test is normal.