Diagnosing gestational diabetes mellitus: use of a glucose screen without administering the glucose tolerance test

To determine if a 1-hour glucose screen value could be identified, above which gestational diabetes mellitus could be diagnosed without the 3-hour oral glucose tolerance test (GTT).

Demographic, historic, obstetric, and neonatal data from 514 singleton pregnancies with glucose screen values at least 140 mg/dL followed by a GTT were reviewed (312 patients with normal GTTs and 202 with gestational diabetes mellitus). Statistical analyses used chi2, Fisher exact, Student t, and Mann-Whitney tests. After determining the optimal glucose screen cutoff point using receiver operating characteristic curve analyses, patients were regrouped according to this value and analyzed further.

The optimal cutoff point for the upper limit of the glucose screen was determined to be 186 mg/dL (95.9% specificity, 98.2% negative predictive value, 36.1% sensitivity, and 19.6% positive predictive value). Comparison of patients with elevated screens and normal GTTs versus those with gestational diabetes revealed significant differences only regarding a history of gestational diabetes mellitus and neonatal hypoglycemia in the studied pregnancy. Those with screens greater than 185 mg/dL behaved like diabetic patients and, when compared with subjects with screens of 140-185 mg/dL, also had a significantly greater proportion of large for gestational age infants.

Patients with 1-hour glucose screens greater than 185 mg/dL have a high probability of gestational diabetes mellitus and the diagnosis can be made without the GTT. Using this approach could allow prompt initiation of therapy without the inconvenience and discomfort of the GTT.