The best time for pregnant women to have a glucose tolerance test is 24-28 weeks of pregnancy. Glucose tolerance is the abbreviation of oral 75g glucose tolerance, also known as OGTT test, and this test is applicable to pregnant women with fasting blood glucose ≥ 5.1mmol/L. If you have the following conditions: 1, age greater than 35 years old; 2, pre-pregnancy obesity or polycystic ovary syndrome; 3, a family history of diabetes mellitus or previous history of gestational diabetes mellitus; 4, unexplained stillbirths, miscarriages, giant babies and other adverse pregnancy and childbirth history; 5, recurrent mycosis fungoides vaginitis during pregnancy. If there are several of the above conditions, even if the fasting blood glucose <5.1mmol / L is recommended to carry out glucose tolerance test at 24-28 weeks of pregnancy, in order to timely detection of a small number of these pregnant women with gestational diabetes mellitus, so as to reduce the adverse prognosis for the mother and child.