Sex hormone-binding globulin in gestational diabetes

Insulin is an important regulator of serum sex hormone-binding globulin (SHBG) concentration which works by inhibiting its production in hepatocytes. Low SHBG level is associated with increased insulin resistance and hyperinsulinemia. Our purpose was to compare maternal serum SHBG level between normal and gestational diabetic pregnant women and to study the relationships between SHBG, SHBG/insulin and SHBG/glucose ratio and several endocrine, metabolic and clinical parameters.

Serum SHBG concentrations were measured in 34 women with gestational diabetes and in 32 matched controls. Glucose, insulin, C-peptide, fructosamine, beta-HCG, cholesterol, triglycerides, HDL cholesterol, LDL cholesterol, apolipoprotein A, apolipoprotein B, total and free T4, total and free estriol, T3 and IGF-1 were measured. Insulin sensitivity was estimated using the short insulin tolerance test.

SHBG, SHBG/insulinemia ratio and SHBG/glucose ratio were significantly lower in the diabetic group (309.54 +/- 112.22 vs 460.54 +/- 144.54, p = 0.00001), (33.55 +/- 16.62 vs 72.56 +/- 66.50, p = 0.0006 using log-transformed values), (5.88 +/- 1.87 vs 3.39 +/- 1.23, p < 0.00001). SHBG was negatively correlated with insulinemia (r = -0.40, p = 0.001), C-peptide (r = -0.41, p = 0.001), glycemia (r = -0.27, p = 0.02), diastolic blood pressure (r = -0.41, p = 0.001) and beta-HCG (r = -0.41, p = 0.001) and positively correlated with LDL-c (r = 0.25, p = 0.04) and apolipoprotein B (r = 0.33, p = 0.007).

SHBG concentrations are lower in gestational diabetic pregnant women and are related to insulin levels but not to peripheral insulin sensitivity. Since insulinemia was similar in normal and gestational diabetic pregnant women, we speculate that gestational diabetes is characterized by a higher peripheral insulin resistance, a fasting normal insulinemia and a higher hepatic insulin sensitivity, at least in other actions than on carbohydrate metabolism. The role of sex steroids, T4 and IGF-1 in regulating SHBG appears to be limited during pregnancy.