The glycosylated hemoglobin (HbA1C) values tend to be less in pregnant women than in non-pregnant, and this is because the average blood glucose concentration tends to be lower in pregnant women. In addition, the rise in red cell mass and the rise in red blood cell turnover during pregnancy contributes to a lower HbA1C. For this reason, frequent monitoring of HbA1C to assess glycemic control during pregnancy in women with GDM may not be useful in those with low HbA1C levels at initial visit. However, its measurement may be helpful in those with overt diabetes with an HbA1C >6.5%.