TOWARD UNIVERSAL CRITERIA FOR GESTATIONAL DIABETES - RELATIONSHIPS BETWEEN SEVENTY-5 AND ONE HUNDRED GRAM GLUCOSE LOADS AND BETWEEN CAPILLARY AND VENOUS GLUCOSE-CONCENTRATIONS

OBJECTIVES: Replacement of the two-step, 100 gm, 3-hour National Diabe tes Data Group procedure by the one-step, 75 gm, 2-hour World Health O rganization 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 ve nous plasma or capillary blood. STUDY DESIGN: After a 75 gm oral gluco se tolerance test 30 gestational diabetics and 30 metabolically health y 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 p eptide. RESULTS: In controls 1-hour maternal glucose levels (112 vs 12 8 mg/dl) and 2-hour levels (104 vs 113 mg/dl) differed significantly a fter a 75 or 100 gm load (paired t test). In gestational diabetes mell itus, however, there was no difference (176 vs 178 mg/dl) but a low in sulin/glucose quotient at 1 hour. Only 2-hour levels differed signific antly (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 loa d. In gestational diabetes mellitus, however, glucose measurement in c apillary blood and venous plasma differed neither in 1-hour levels (17 9 vs 174 mg/dl) nor in 2-hour levels (142 vs 139 mg/dl). CONCLUSION: I n metabolically healthy women both different loading and different blo od fractions lead to statistically different blood glucose levels at 1 and 2 hours. In gestational diabetes mellitus, however, 1-hour glucos e levels do not differ after a 75 or 100 gm load or after glucose meas urement in capillary blood or venous plasma. This is due to elevated i nsulin resistance shown by a low insulin/glucose quotient at 1 hour. F or comparison of tests in gestational diabetes mellitus only, 2-hour v alues must be adjusted by 16 mg/dl after different loading.