Glucose tolerance screens for gestational diabetes. Glucose tolerance is necessary during pregnancy. Since pregnant women are not sensitive to insulin during pregnancy, they are prone to abnormal glucose metabolism and develop gestational diabetes. Gestational diabetes causes adverse effects on pregnant women such as susceptibility to infections, obstructed labor, and excessive amniotic fluid, as well as adverse effects on the fetus such as macrosomia and fetal malformations, so a glucose tolerance is very necessary. Through glucose tolerance test, pregnant women with high blood glucose can be detected in time. For pregnant women with mild condition, they can control their blood glucose by adjusting their diets; for pregnant women with severe condition, they can be treated with insulin to avoid more serious complications. Therefore, it is necessary to do glucose tolerance test during pregnancy, and it is recommended that pregnant women should undergo glucose tolerance test under the guidance of doctors during 25 to 28 weeks of pregnancy to clarify whether they are combined with gestational diabetes.