OBJECTIVES The aim of the study was to examine if the glicated haemoglobin (HbA1C) is useful as an indicator of disturbances of the carbohydrate metabolism in women who suffered from Gestational Diabetes Mellitus (GDM), and for prediction of the macrosomic infants. MATERIAL AND METHODS The examination was performed on 163 GDM women, who were treated in Diabetic Care Unit (1996-98) in Research Institute CZMP in Lódź. GDM was diagnosed between 20 and 32 week of gestation, on the ground of 50 g Glucose Challenge Test (GCT) and 2-hour glucose tolerance test (75OGTT), according to WHO. HbA1C was examined during the first visit in hospital. All women were distributed into two groups: 120--treated with diet alone (G1), 43--treated also with insulin (G2). All the parameters were statistically analized. RESULTS Patients from G2 group were older and had higher glucose values in all diagnostic tests then patients from G1 group. The average HbA1C level in the whole GDM group was 5.9 +/- 1.0% (min. 4.3%; max 9.6%) and was substantially higher in G2 (6.5 +/- 0.9%) then G1 (5.7 +/- 1.0%): p < 0.05. The HbA1C level correlated with fasting glycemia and 1-hour 50GCT (p < 0.05) and did not correlated with 2-hour 75OGTT. We found the relationship between newborns body weight and 2-hour 75OGTT only in G2 group, but newborns body weight did not correlated with HbA1C level. There were no correlation between GDM duration and HbA1C level. CONCLUSIONS 1. Glycosylated haemoglobin can not be the indicator of appearance the fetuses macrosomy. 2. The increased HbA1C level is predictive value for insulin treatment. 3. Body weight of children from insulin treated GDM mothers is connected with fasting and 2-hour 75OGTT glucose level.