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 (IS_OGTT) or fasting glucose/insulin levels (IS_QUICKI and IS_HOMA) 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 (IS_CLAMP) 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 IS_CLAMP and IS_OGTT (r² = 0.74, P < 0.0001), IS_QUICKI (r² = 0.64, P < 0.0001), and IS_HOMA (r² = 0.53, P < 0.0001). The IS_OGTT provided a significantly better correlation (P < 0.0001) than either IS_QUICKI or IS_HOMA. 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 IS_CLAMP and IS_OGTT 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 IS_OGTT 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.