The effect of taking metformin in pregnancy on the fetus is unknown, there is no saying whether it is good for the fetus or not, and this drug is not yet a first-line drug for controlling blood sugar in China. Metformin is a common hypoglycemic drug for patients with type 2 diabetes mellitus who have poor hypoglycemic effect after simple dietary control or exercise therapy, and it can also be used in combination with sulfonylureas or insulin to control blood glucose. Common adverse reactions include nausea, vomiting, diarrhea, fatigue, abdominal distension, headache and so on. For pregnant and lactating women, metformin is not routinely used in China, and subcutaneous insulin is generally applied. Contraindications to the use of the drug are type 2 diabetes mellitus with ketoacidosis, diabetes mellitus with serious chronic complications, serious infections and traumas, major surgery, serious functional insufficiency of vital organs, poor general condition, vitamin B12 or folic acid or iron deficiency, before radiography, alcoholics and so on. The efficacy and safety of this drug are not known, and its effect on the fetus is unknown, as no adequate, rigorously controlled clinical studies have been conducted in pregnant women. The use of the drug should be under the guidance of a specialist and should not be self-administered.