Objective: The purpose of this study was to investigate the insulin response to a 3-hour oral glucose tolerance test and to compare the insulin levels in the gestational diabetes mellitus and single abnormal test value groups with a nondiabetic control group.
Study design: One hundred ten Turkish women with uncomplicated pregnancy participated in this prospective controlled study between 24 to 28 weeks of gestation. A 100-g 3-hour oral glucose tolerance test was given, and glucose and insulin plasma levels were assayed. The subjects were classified according to established criteria. Early-phase insulin secretion was assessed by the insulinogenic index. Total insulin secretion was assessed by mean insulin level during the oral glucose tolerance test; insulin resistance was assessed by fasting insulin concentration and by the use of the homeostasis model. Data were analyzed by the Student t test and 1-way analysis of variance, with posthoc Bonferroni correction.
Results: The fasting insulin levels of patients with normal oral glucose tolerance test results were significantly lower than those of patients with gestational diabetes mellitus and a single value abnormality (P <.001 and P <.005, respectively). The insulinogenic index as a marker of early-phase insulin secretion was significantly lower in gestational diabetes mellitus, compared with that of patients with normal oral glucose tolerance test results (P <.05). The worsening of glycemic profile from normal oral glucose tolerance test results to gestational diabetes mellitus was associated with an increase in the homeostasis model; no significant difference was found between gestational diabetes mellitus and a single value abnormality group in terms of both the homeostasis model and the insulinogenic index. Values for total insulin secretion were highest in gestational diabetes mellitus, followed by the single value abnormality group, both significantly differing from the values of patients with normal oral glucose tolerance test results (P <.001 and P <.005, respectively).
Conclusion: In this prospective study of Turkish subjects, we found a striking similarity in terms of patient characteristics between the gestational diabetes mellitus group and the single value abnormality group. Additionally, when we used fasting insulin level and insulin resistance as 2 separate criteria of analysis, patients with single value abnormality were indistinguishable from patients with gestational diabetes mellitus; both groups were significantly different from the normal oral glucose tolerance test group. Our findings suggest that a single abnormal test value on an oral glucose tolerance test should be regarded as a pathologic finding and that the patient with a single abnormal test value may be treated similarly to the patient with gestational diabetes mellitus.