Final answer:
The criterion for a diagnosis of gestational diabetes is a fasting plasma glucose level of more than 92 mg/dL but less than 126 mg/dL, which is lower than the threshold for a general diabetes diagnosis.
Step-by-step explanation:
The criterion for a diagnosis of gestational diabetes is a fasting plasma glucose level of more than 92 mg/dL but less than 126 mg/dL. This is specific to gestational diabetes screening and can differ from the criteria used for the general diagnosis of diabetes mellitus.
For a general diabetes diagnosis, fasting blood glucose levels are considered normal if they are below 100 mg/dL. A fasting glucose level between 100 and 125 mg/dL indicates pre-diabetes, and a level of 126 mg/dL or higher after fasting indicates a diagnosis of diabetes.
In the context of a glucose tolerance test (GTT), while confirming diabetes mellitus, a person whose fasting blood glucose is within normal ranges, may still exhibit a steep rise in blood sugar upon oral glucose intake which does not return to normal within 2½ hours, indicating diabetes mellitus.