A population of 40 mother-newborn pairs with a wide range of birth weight has been studied. Seventeen of the mothers were diabetic, while the other 23 were normal pregnant women. The chronic blood glucose levels were assessed in the mothers through the percentage of glycosylated hemoglobin (HbA1) at delivery. The functional activity of the pancreatic β-cells in the newborns was estimated through the concentration of insulin and C-peptide in the cord blood. Maternal HbA1 was not quantitatively related to the birth weight ratio. In contrast, both insulin and C-peptide correlated significantly with it. Is is concluded that in populations with a good metabolic control, blood glucose levels, as measured by HbA1 are not the major determinant of fetal growth.