Forty insulin-dependent diabetic women in the first trimester of pregnancy were studied. Fetal crown-rump length was measured by ultrasound and related to maternal hemoglobin A1c. Thirty mothers with normal size fetuses had an average hemoglobin A1c level of 7.8%. Ten mothers had fetuses that were smaller than normal (equivalent to eight to 14 days less growth) and also had higher hemoglobin A1c, 8.9% (P less than .05), indicating a more poorly controlled diabetes. Careful metabolic compensation in very early diabetic pregnancy should therefore be attempted to prevent induction of early fetal growth delay.