The effects of high blood sugar on the fetus of a pregnant woman include: macrosomia, preterm labor, fetal growth restriction, fetal malformation, and comorbidities of gestational diabetes mellitus. 1. Macrosomia: High blood sugar in pregnant women can enter the baby’s body through the placenta, resulting in hyperglycemia and excessive growth rate of the fetus, and then there may be macrosomia. 2. Preterm labor: Increased blood sugar in pregnant women may lead to excessive production of amniotic fluid and may also cause gestational hypertension, which may lead to preterm labor. 3. Fetal growth restriction: A significant increase in blood glucose levels in pregnant women may lead to abnormal changes in blood vessels, which may have a certain impact on the blood supply to the fetus, and fetal growth restriction may occur. 4. Fetal malformation: Increased blood glucose may cause hypoxia or metabolic disorders, resulting in increased probability of congenital malformation of the fetus. 5. Gestational diabetes comorbidities: Pregnant women with high blood glucose, i.e., diagnosed with gestational diabetes, may develop comorbidities such as gestational hypertension, mycosis vaginalis, and infections. High blood glucose may have significant effects on the pregnant woman as well as the fetus, and requires appropriate treatment under the guidance of a medical professional.