Clinically Useful Estimates of Insulin Sensitivity During Pregnancy

Abstract

OBJECTIVE—We examined whether selected indexes of insulin sensitivity derived from an oral glucose tolerance test (ISOGTT) or fasting glucose/insulin levels (ISQUICKI and ISHOMA) can be used to predict insulin sensitivity in women before and during pregnancy. RESEARCH DESIGN AND METHODS—A 2-h euglycemic-hyperinsulinemic clamp (5 mmol/l glucose, 40 mU · m−2 · min−1 insulin) and a 120-min oral glucose tolerance test (75 g load pregravid, 100 g pregnant) were repeated on 15 women (10 with normal glucose tolerance [NGT] and 5 with gestational diabetes mellitus [GDM]) pregravid and during both early (12–14 weeks) and late (34–36 weeks) pregnancy. An index of insulin sensitivity derived from the clamp (ISCLAMP) was obtained from glucose infusion rates adjusted for change in fat-free mass and endogenous glucose production measured using [6,6-2H2]glucose. RESULTS—Univariate analysis using combined groups and periods of pregnancy resulted in significant correlations between ISCLAMP and ISOGTT (r2 = 0.74, P < 0.0001), ISQUICKI (r2 = 0.64, P < 0.0001), and ISHOMA (r2 = 0.53, P < 0.0001). The ISOGTT provided a significantly better correlation (P < 0.0001) than either ISQUICKI or ISHOMA. Multivariate analysis showed a significant group effect (P < 0.0003) on the prediction model, and separate equations were developed for the NGT (r2 = 0.64, P < 0.0001) and GDM (r2 = 0.85, P < 0.0001) groups. When subdivided by period of pregnancy, the correlation between ISCLAMP and ISOGTT pregravid was r2 = 0.63 (P = 0.0002), during early pregnancy was r2 = 0.80 (P < 0.0001), and during late pregnancy was r2 = 0.64 (P = 0.0002). CONCLUSIONS—Estimates of insulin sensitivity from the ISOGTT during pregnancy were significantly better than from fasting glucose and insulin values. However, separate prediction equations are necessary for pregnant women with NGT and women with GDM.