Abstract: Objective：To establish the normal reference interval in the second trimester pregnant women of glycosylated hemoglobin (HbA1c) in the Tianjin Central Hospital of Gynecology Obstetrics, and evaluate the application value of HbA1c combined with fasting blood glucose (FPG) in the detection of gestational diabetes mellitus (GDM). Methods：According to the GDM diagnostic criteria of International Association of Diabetes and Pregnancy Study Groups (IADPSG) recommended, 196 GDM pregnant women and 320 health control with 75 g oral glucose tolerance test (OGTT) examination in our hospital from May 2016 to December 2016 during 24 to 28 weeks of pregnancy were enrolled, and the related clinical data were collected. Results：①The age, pre-pregnancy weight and pre-pregnancy BMI of the GDM group were significantly higher than those of health control group(P＜0.01), no significant difference were found in the gestational age and height between the two groups (P＞0.05). ②The average value of HbA1c, the blood glucose levels of OGTT in GDM women were significantly higher than the health control group (P＜0.01). ③The HbA1c level of all the 320 healthy pregnant women was in normal distribution. The HbA1c reference interval of the normal pregnant women in the second trimester of pregnancy was 4.4%-5.8%. ④The highest sensitivity and specificity in prediction of GDM were 44.9% and 77.5% respectively when the HbA1c was 5.35%. The ROC curve area of HbA1c in diagnosis of GDM was 0.665 (95%CI: 0.617-0.713); The curve area of the HbA1c（≥5.35%）combined with FPG（≥5.1 mmol/L） in diagnosis of GDM was 0.933 (95%CI: 0.909-0.957). Conclusions：The normal reference range of HbA1c of the pregnant women in our hospital was established. HbA1c combined with FPG detection was simple and convenient, and can be used as a powerful supplement to GDM diagnosis.

Key words: Diabetes, gestational, Hemoglobin A, glycosylated, Fasting plasma glucose, Glucose tolerance test