Glycemic control is an important issue in gestational diabetes mellitus (GDM) and in diabetic pregnant women. We determined the reference intervals of glycated albumin (GA) and hemoglobin A1c (HbA1c) as glycemic control markers in healthy Japanese pregnant women and analyzed their time courses and factors that influence these variables during pregnancy. 676 women were screened for the present study. After the exclusion of non-pregnant and puerperal women, 574 women were studied to determine the reference intervals. HbA1c, GA, casual plasma glucose, urinary glucose, urinary protein, and body mass index (BMI) (non-pregnancy) were measured. HbA1c levels significantly decreased in the second trimester of pregnancy and increased in the third trimester, while GA levels significantly decreased towards the third trimester. Casual plasma glucose levels decreased in the first trimester and subsequently remained constant. The reference intervals of GA and HbA1c in the healthy pregnant women were 11.5-15.7% and 4.5-5.7%, respectively. GA levels were lower (p<0.01) and HbA1c levels were higher (p<0.05) in pregnant women with proteinuria. In the obese group, GA levels were lower (p<0.01) than those of the control group (18.5≤ BMI <25kg/m²), and HbA1c levels were higher (p<0.01) than those of the control group. On the basis of the results of this multicenter study, the reference intervals of GA and HbA1c in healthy Japanese pregnant women were determined. Strict glycemic control is essential to reduce perinatal complications. GA appears to be a useful marker for pregnant women, since it can be measured easily and changes rapidly and markedly.