Oral glucose tolerance test (OGTT)-based measures of insulin secretory response have not been validated in pregnancy.
In a secondary analysis of a longitudinal study, participants were studied pre-pregnancy (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), insulin/glucose area under the curve (AUCins/AUCglu), 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.
Stumvoll was the only OGTT-based measure that was significantly correlated with first phase insulin response prior to and across gestation (pre: r=0.44, P=0.01; early: r=0.67, P=0.0001; late: r=0.67, P=0.0001). In early and late pregnancy, AUCins/AUCglu had the strongest correlation with first phase insulin response (early: r=0.79, P<0.0001; late: r=0.69, P<0.0001), but was not significantly correlated pre-pregnancy. IGI and CIR were significantly correlated with first phase insulin response pre-pregnancy (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-B was the weakest correlate of first phase insulin response. Stumvoll and AUCins/AUCglu recapitulated the longitudinal changes in insulin secretory response observed by IVGTT.
Stumvoll and AUCins/AUCglu are valid OGTT-based insulin secretory response measures for pregnancy studies.

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