Pregnant women with normal insulin secretion function generally do not have large changes in blood glucose in late pregnancy; while for pregnant women with limited insulin secretion, blood glucose will increase and gestational diabetes may occur or aggravate the existing diabetes. In the early and middle stages of pregnancy, with the increase of gestational weeks, fetal demand for nutrients increases, through the placenta from the mother to obtain glucose is the main source of fetal energy, pregnant women plasma glucose levels with the progression of pregnancy and decrease. In the middle and late stages of pregnancy, estrogen, progesterone, cortisol and other antagonistic insulin-like substances in the body increase, pregnant women’s sensitivity to insulin decreases, at this time, if the compensatory secretion of insulin is insufficient, can not compensate for these physiological changes and make the blood glucose rise, easy to gestational diabetes mellitus or aggravation of the original diabetes mellitus. It is recommended that pregnant women monitor their blood glucose regularly during late pregnancy and go to the hospital in time when blood glucose abnormalities occur.