There are two types of diabetes mellitus during pregnancy: one is preexisting diabetes mellitus before pregnancy and is diabetes mellitus combined with pregnancy. The other is gestational diabetes, which occurs during pregnancy or when abnormal glucose tolerance is first detected. The former is present before pregnancy and easily attracts the attention of pregnant women. The latter is highly negligible because it is mostly asymptomatic. Therefore, it is important to check blood sugar regularly during pregnancy, especially after 20 weeks, to avoid as much as possible the adverse effects of this disease on the pregnant woman and the fetus. Causes of abnormal blood sugar during pregnancy: I. Hormones hinder secretion. During pregnancy, the placenta of the mother-to-be will secrete hormones that can counteract the production of insulin, and the reduction of insulin secretion will easily cause the mother-to-be to have high blood sugar during pregnancy, which will endanger the health of the baby. Secondly, unreasonable diet structure, disease from the mouth, unreasonable diet structure will also cause high blood sugar of the mother-to-be during pregnancy. The large intake of high-sugar and high-fat food during pregnancy, the stimulation of food increases the secretion of insulin, and when the function of insulin can not withstand this pressure, the secretion of insulin can not meet the needs of the mother-to-be’s body, it will cause the mother-to-be to have high blood sugar during pregnancy. Third, overweight.