Defective Plasma Insulin Response during Prednisolone Glucose Tolerance Tests in Subclinical Diabetic Mothers of Heavy Infants

Abstract

Plasma glucose and immuno-reactive insulin (IRI) were measured during 4-hour oral GTT and prednisolone glucose tolerance tests (PGTT) in 36 women suspected of having diabetes mellitus because they had recently delivered an infant weighing 9 lb. or more. The results were compared to similar tests performed on 10 nonobese women who had given birth to normal weight infants. All diabetes suspects had normal GTT, and the total IRI response (area circumscribed by the plasma insulin response curve) was similar to the control group. During PGTT, 17 suspects had a mild diabetic curve despite the finding that total plasma IRI response remained similar to the control individuals and the 19 suspects who had normal PGTT. Examination of the pattern of the hormonal response, however, revealed that in the subclinical diabetic group plasma insulin levels at 30 min. during PGTT were subnormal relative to abnormally high plasma glucose concentrations at this time interval. This defect was not observed during GTT, when all individuals had normal carbohydrate tolerance. The majority of women who delivered large infants were also moderately obese whether or not diabetes was present. The results of these studies indicate that most women with subclinical diabetes mellitus who deliver large infants will escape detection in the immediate postpartum period if the evaluation is limited to a standard oral GTT. The impaired glucose tolerance elicited during PGTT would appear to be directly related to a defective insulin response during the initial 30-60 min. following oral glucose administration and is spontaneously reversible when a diabetogenic stress such as that produced with oral glucocorticoids and presumably pregnancy is not present.