SummaryTotal glycosylated haemoglobin (Hb A1 (a + b + c)) was measured several times during the third trimester of pregnancy in 40 insulin-treated diabetics and the results compared with the patients' glucose control and fetal outcome. In spite of poor glucose control, 2 patients were found who had normal glycosylated haemoglobin levels throughout; both produced macrosomic babies who became hypoglycaemic. Conversely, 4 patients with apparently good inpatient glucose control were found to have abnormal glycosylated haemoglobin and also delivered abnormal infants. Poor fetal outcome in terms of macrosomic or hypoglycaemia and high cord C-peptide concentration reflecting pancreaticβ-cell hyperplasia was sufficiently well associated with abnormal glycosylated haemoglobin concentration to conclude that its measurement is a useful additional test for monitoring diabetic pregnancy