Pregnant women with high fasting blood glucose 5.8mmol/L but normal postprandial blood glucose are usually considered to be suffering from gestational diabetes mellitus, gestational diabetes mellitus with high fasting blood glucose but normal postprandial blood glucose is considered to be caused by the dawn phenomenon or the Sumuje reaction. The normal fasting blood glucose of pregnant women during pregnancy should be less than 5.1mmol/L, so the fasting blood glucose of 5.8mmol/L is on the high side. Gestational diabetic patients with high fasting blood glucose but normal postprandial blood glucose are considered to be caused by the dawn phenomenon, i.e., the blood glucose control is stable at night, but the imbalance of secretion of various hormones in the early morning will lead to the elevation of fasting blood glucose. In addition, it may also be caused by the hematoxylin reaction, i.e., the patient has a hypoglycemic episode at night, and then the blood sugar rebound in the early morning leads to an increase in fasting blood glucose. Nighttime blood glucose can be monitored to clarify the cause of high fasting blood glucose. Pregnant women with elevated fasting blood glucose but normal postprandial blood glucose are advised to go to the hospital for a doctor’s judgment.