The objective of the study was to assess the incidence of gestational diabetes among black women according to various cut-off values of the glucose challenge test.

We performed a retrospective chart review of black patients who had a 50-g, 1-hour glucose challenge test between 24 and 28 weeks' gestation of 130 mg/dL or higher followed by a 100-g, 3-hour glucose tolerance test. Results were categorized in 10-mg/dL increments. Gestational diabetes was diagnosed by 2 or more abnormal values using the Carpenter-Coustan criteria.

The study included 387 patients. The incidence of gestational diabetes diagnosed overall in all patients with a glucose challenge test of 130 mg/dL or higher was 31.2%. The incidence of gestational diabetes in individuals with a challenge test in the range of 130 to 140 mg/dL was 10.7%. The incidence of gestational diabetes with a screening test of 180 mg/dL or higher was 72.0%.

Our data support the use of 130 mg/dL as the threshold for a positive glucose challenge test and suggest the use of a glucose tolerance test to confirm the diagnosis of gestational diabetes for screening values up to 200 mg/dL.