Toward universal criteria for gestational diabetes: relationships between seventy-five and one hundred gram glucose loads and between capillary and venous glucose concentrations.

Abstract

Replacement of the two-step, 100 gm, 3-hour National Diabetes Data Group procedure by the one-step, 75 gm, 2-hour World Health Organization oral glucose tolerance test has been hindered by a paucity of data comparing the two tests during pregnancy. The current series compared 100 gm and 75 gm glucose loads and glucose measurements in venous plasma or capillary blood. After a 75 gm oral glucose tolerance test 30 gestational diabetics and 30 metabolically healthy pregnant women were randomly assigned to a second 75 or 100 gm test within 3+/-1.3 (mean+/-SD) days. Glucose levels at both tests was measured in capillary blood and venous plasma, as were insulin and C peptide. In controls 1-hour maternal glucose levels (112 vs 128 mg/dl) and 2-hour levels (104 vs 113 mg/dl) differed significantly after a 75 or 100 gm load (paired t test). In gestational diabetes mellitus, however, there was no difference (176 vs 178 mg/dl) but a low insulin/glucose quotient at 1 hour. Only 2-hour levels differed significantly (133 vs 149 mg/dl). In controls glucose measurement in capillary blood and venous plasma differed significantly at 1 hour (126 vs 115 mg/dl) and 2 hours (111 vs 104 mg/dl) independently of the glucose load. In gestational diabetes mellitus, however, glucose measurement in capillary blood and venous plasma differed neither in 1-hour levels (179 vs 174 mg/dl) nor in 2-hour levels (142 vs 139 mg/dl). In metabolically healthy women both different loading and different blood fractions lead to statistically different blood glucose levels at 1 and 2 hours. In gestational diabetes mellitus, however, 1-hour glucose levels do not differ after a 75 or 100 gm load or after glucose measurement in capillary blood or venous plasma. This is due to elevated insulin resistance shown by a low insulin/glucose quotient at 1 hour. For comparison of tests in gestational diabetes mellitus only, 2-hour values must be adjusted by 16 mg/dl after different loading.