Objective: To compare pregnancy outcomes in women diagnosed as having class A1 gestational diabetes with those of a group with a normal 3-hour glucose tolerance test (GTT) to assess morbidities attributable to glucose intolerance.

Methods: Selective 50-g GTT identified pregnant women who received a 3-hour GTT. Over a 16-month period, 159 women were diagnosed as having class A1 gestational diabetes according to the National Diabetes Data Group criteria. During the latter 12 months of this time period, 151 women who had a normal GTT result were identified for comparison.

Results: There were statistically significant differences in age and the development of peripartum hypertension in women with class A1 gestational diabetes compared with the normal 3-hour GTT group. There were no significant differences in any neonatal outcome variable, including percent delivering large for gestational age (LGA) neonates in women with A1 diabetes compared to controls. Overall, 111 (36%) of the 310 neonates were classified as LGA, a rate more than double that in the singleton population in our hospital. Maternal weight, parity, and a history of a previous macrosomic infant were significantly associated with LGA outcome. Mean maternal weight was the same in the two GTT groups, implying an independent effect on fetal size. Obstetric interventions were not significantly different between the groups, so differences in intervention could not account for the lack of difference in outcome variables. The impact of dietary counseling in the class A1 diabetic women is also an unlikely explanation for the lack of differences in outcome. Within the normal-GTT group, women with one abnormal 3-hour value had a frequency of LGA infants similar to that of women with all normal 3-hour GTT values. These results suggest that there is a selection effect of screening for glucose intolerance that may relate more to other risk factors for LGA outcome than to glucose intolerance. Maternal obesity is an independent and more potent risk factor for large infants than is glucose intolerance.

Conclusion: The diagnosis of class A1 gestational diabetes is not significantly associated with obstetric and perinatal morbidities. A nondiscriminating diagnostic test undermines the validity of population screening for glucose intolerance.