During a 100 g oral glucose tolerance test for gestational diabetes, which reading is abnormal at the 1-hour mark?

• A. Fasting greater than 95 mg/dL
• B. 1 hour greater than 180 mg/dL
• C. 2 hour greater than 155 mg/dL
• D. 3 hour greater than 140 mg/dL

Answer: (B)

Ingested glucose handling in pregnancy is assessed with a 100 g oral glucose tolerance test, using specific thresholds at each time point. At the 1-hour mark, a reading of 180 mg/dL or higher is considered abnormal. The commonly used Carpenter-Coustan thresholds are: fasting ≥95 mg/dL, 1 hour ≥180 mg/dL, 2 hours ≥155 mg/dL, and 3 hours ≥140 mg/dL. While diagnosis of gestational diabetes often requires two or more values to be abnormal, the key point for the 1-hour measure is that 180 mg/dL or higher is the abnormal threshold.