Lowering the threshold for the diagnosis of gestational diabetes

Our purpose was to determine whether lowering the diagnostic threshold for gestational diabetes mellitus on 3-hour 100 gm oral glucose tolerance testing will select a population at risk for adverse perinatal outcome.

In this retrospective study 434 patients with an abnormal 50 gm glucose screen result (> or = 140 mg/dl) underwent a standardized 3-hour oral glucose tolerance test. The results were stratified according to maternal weight and the criteria recommended by Sacks or Carpenter. Birth weight and rate of macrosomia were the primary perinatal outcome variables analyzed.

Analysis of the data set stratified according to the Sacks criteria revealed results very similar to the Carpenter criteria data set. Patients who would have been newly diagnosed with gestational diabetes mellitus only if the lowered criteria were used (group 2) were older and heavier. No other variable comparisons achieved statistical significance. When the same patients were stratified according to prepregnancy weight, overweight patients were older, gained less weight during the third trimester, underwent cesarean section more often, and had higher cumulative maternal morbidity. Regression analysis showed that the degree of hyperglycemia did not predict macrosomia or influence birth weight, but prepregnant maternal body mass index was associated with macrosomia.

Fetal macrosomia is influenced by maternal prepregnant body mass index. Lowering the glucose tolerance test threshold would result in overdiagnosis of gestational diabetes mellitus without improving perinatal outcome.