Oral Glucose Tolerance Test-based Measures of Insulin Secretory Response in Pregnancy

Background Oral glucose tolerance test (OGTT)-based measures of insulin secretory response have not been validated in pregnancy. Methods In a secondary analysis of a longitudinal study, participants were studied prepregnancy (n = 40), in early pregnancy (n = 36; 12-14 weeks' gestation), and in late pregnancy (n = 36; 34-36 weeks' gestation). Participants underwent an OGTT, an intravenous glucose tolerance test (IVGTT), and a hyperinsulinemic-euglycemic clamp at each timepoint. We calculated homeostatic model assessment of beta-cell function (HOMA-2B), insulinogenic index (IGI), corrected insulin response (CIR), ratio of the area under the insulin curve and the area under the glucose curve (AUC(ins)/AUC(glu)), and Stumvoll first-phase estimate (Stumvoll) from OGTT insulin and glucose levels. We used Pearson correlation to compare measures from OGTT and IVGTT. We used mixed effects models to examine longitudinal changes in insulin secretory response. Results Stumvoll was the only OGTT-based measure that was significantly correlated with first-phase insulin response prior to and across gestation (prepregnancy: r = 0.44, P = 0.01; early pregnancy: r = 0.67, P = 0.0001; late pregnancy: r = 0.67, P = 0.0001). In early and late pregnancy, AUC(ins)/AUC(glu) had the strongest correlation with first-phase insulin response (early pregnancy: r = 0.79, P < 0.0001; late pregnancy: r = 0.69, P < 0.0001) but was not significantly correlated prepregnancy. IGI and CIR were significantly correlated with first-phase insulin response prepregnancy (IGI: r = 0.50, P = 0.005; CIR r = 0.47, P = 0.008) and in late pregnancy (IGI: r = 0.68, P = 0.0001; CIR r = 0.57, P = 0.002) but not in early pregnancy. HOMA-2B was the weakest correlate of first-phase insulin response. Stumvoll and AUC(ins)/AUC(glu) recapitulated the longitudinal changes in insulin secretory response observed by IVGTT. Conclusions Stumvoll and AUC(ins)/AUC(glu) are valid OGTT-based insulin secretory response measures for pregnancy studies.

Automated summary

The study found that Stumvoll and AUC(ins)/AUC(glu) are valid OGTT-based measures of insulin secretory response during pregnancy, and can effectively reflect the changes in insulin secretion.