Aims: We hypothesized that an increased serum insulin level in early pregancy reflects an increased demand on the compensatory capacity of the pregnant woman, and can serve as a predictor of gestational diabetes mellitus (GDM).
Methods: A 2-h, 75-g oral glucose tolerance test (OGTT), with fasting and 2-h postprandial serum insulin determination, was performed in 71 pregnant women with one or more risk factors for GDM before gestation week 16. In 64 patients, subsequent OGTTs were performed at gestation weeks 24-28, and in the event of a negative result, at gestation weeks 32-34.
Results: Insulin determination at fasting and at 120 min had sensitivities of 69.2% and 92.3%, and specificities of 96.4% and 85.7%, respectively, for the prediction of GDM at gestation weeks 24-28. The sensitivities decreased to 33.3% and 75.0%, respectively, for the prediction of GDM at gestation weeks 32-34. Insulin determination at fasting and at 120 min had positive predictive values of 0.90 and 0.75, respectively, for the prediction of GDM at gestation weeks 32-34. The negative predictive values of fasting and 120-min serum insulin determination at gestation week < or = 16 were 0.87 and 0.96, respectively, for the prediction of GDM at gestation weeks 24-28. Increased serum insulin levels both at fasting and 120 min before gestation week 16 were very strong predictive factors for GDM by gestation weeks 32-34 with an odds ratio of 16.6 and 13.3, respectively.
Conclusions: Serum insulin determination at gestation week < or = 16 is an easy and reliable method with which to predict GDM in a high-risk group. Despite a negative OGTT, patients with an elevated fasting and/or 120-min serum insulin level at gestation week < or = 16 should be managed in the same way as those with GDM. Considering the very high negative predictive value of the method, patients with a normal fasting and/or 120-min serum insulin level at gestation week < or = 16 should undergo an OGTT only at gestation weeks 32-34.