Gestational diabetes mellitus is mainly caused by increased glucose requirement, increased insulin resistance and relative deficiency of insulin secretion. 1. Increased glucose requirement: with the increase of pregnancy weeks, the demand of fetus for nutrition increases, and the mother’s body consumes more glucose, thus eating more. Due to the relative insufficiency of insulin secretion at this time, the body of pregnant women cannot fully metabolize these sugars, causing an increase in blood glucose. 2. Insulin resistance and relative insufficiency of secretion: in the middle and late stages of pregnancy, pregnant women’s bodies increase the number of substances that antagonize insulin, the body’s sensitivity to insulin decreases, and the demand for insulin will increase accordingly. For pregnant women with limited insulin secretion, they can’t compensate for this physiological change during pregnancy and make their blood sugar rise, resulting in gestational diabetes mellitus. It is recommended that patients with gestational diabetes go to the hospital in time and under the guidance of the doctor for standardized treatment, so as not to delay the condition and lead to adverse consequences.