Glucose tolerance and insulin secretion in pregnancy

The authors have studied the behaviour of plasma glucose, insulinaemia and insulin-glucose ratio in 2 groups of pregnant women with BMI values > or = or <26, respectively. Each group was divided into 3 subgroups on the basis of an oral glucose tolerance test (OGTT) response: GIGT (gestational impaired glucose tolerance), GD (gestational diabetes), and C (normal controls). Data from non-obese pregnant women demonstrate that both basal and OGTT-stimulated glucose levels were significantly different in all subgroups. The total insulin amount in the GIGT and GD subgroups is quite similar to or greater than the controls, but with a significant reduction of the insulin-glucose ratio. In GD also an absolute deficiency of insulin rise at 30 min during the glucose load, as in subjects with Type 2 diabetes mellitus (T2DM), was observed. The behaviour of these parameters in obese pregnant women seems to be similar, even though with some significant differences: in these subjects, there is a less clear-cut differentiation among all subgroups, and the appearance of gestational diabetes is not accompanied by a significant decrease of insulin secretion at 30 min. Our data seem to demonstrate that insulin resistance with an inadequate hyperinsulinaemia is a common factor for the alterations of carbohydrate metabolism during pregnancy. Only in the non-obese patients with gestational diabetes, is there an absolute defect of early insulin response to the glucose load, as it is seen in T2DM.