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The oxygenation status of normal and diabetic (White's classification A and B) mothers and their neonates was investigated. The diabetic patients had significantly increased maternal total haemoglobin and P50 values and the percentage of fetal haemoglobin was increased in cord blood taken at delivery in this group. There was a significant positive correlation between maternal P50 values and the percentage of fetal haemoglobin in cord blood. The cord blood 2,3-diphosphoglycerate, inorganic phosphate and P50 values were also increased in neonates born to diabetic mothers and these infants had a significantly increased birth weight ratio. The results are consistent with the presence of fetal hypoxaemia in the late third trimester of diabetic pregnancy in which obvious maternal vascular disease has been excluded.

A single measurement of total maternal glycosylated haemoglobin (Hb A1) in the late third trimester of a diabetic pregnancy is of limited value in assessing diabetic control. There was no significant correlation between maternal Hb A1 values and neonatal C-peptide values or birth-weight ratios. An isolated Hb A1 measurement is not sufficiently sensitive to monitor the control of diabetes during pregnancy nor is it useful in predicting perinatal outcome.

Increased cord blood C-peptide levels in neonates born to mothers with gestational diabetes (GD) were directly correlated with the increased relative birth weight ratio (BWR) of these neonates. In addition, the percentage oxygen saturation of the cord blood was inversely correlated with cord blood C-peptide levels and with the relative BWR. These correlations were absent in neonates delivered to normal mothers. The results indicate the presence of both hyperinsulinaemia and mild hypoxaemia in neonates of mothers with GD. In poorly controlled diabetic pregnancy this hypoxaemia may constitute an important fetal risk factor.

Acetylation of fetal haemoglobin, probably a post-translational, intracellular, enzyme-mediated reaction, depends upon an adequate supply of glucose and oxygen to the fetus and the nature of the diabetes (if present) in the mother. These complicating factors limit the general usefulness of acetylated fetal haemoglobin assay in fetal assessment.

Birth weight ratios (BWRs) and cord blood C-peptide values were significantly higher in neonates born to mothers with well-controlled gestational diabetes (GD) than in those born to mothers with well-controlled established diabetes (ED) or mothers with normal results on glucose tolerance testing. The neonates born to the ED mothers had the highest cord blood acetylated fetal haemoglobin (Hb F1) values, and these values correlated with cord C-peptide values. The cord C-peptide values in the GD group correlated with BWRs, but not with Hb F1 values. These results suggest differential tissue utilization of glucose in neonates born to mothers with different types of diabetes.