If you're being tested for gestational diabetes, your doctor will consider the results of each blood glucose test. At Mayo Clinic, if your blood glucose level is higher than 140 mg/dL (7.8 mmol/L) after the one-hour test, your doctor will recommend the three-hour test. If your blood glucose level is higher than 190 mg/dL (10.6 mmol/L) after the one-hour test, you'll be diagnosed with gestational diabetes.