The weight of a fetus at 31 weeks is normal at about 1750g, but there are individual differences. At 31 weeks of gestation, which is the late stage of pregnancy, the ultrasound suggests that the fetal biparietal diameter is about 7.7cm, femur length is 6.0cm, abdominal circumference is 26.9cm, and the estimated weight is about 1750g which is normal. When the ultrasound suggests that the fetus is small or large, it is necessary for the physician to double-check the week of gestation, and eugenic tests, immune factor tests and blood glucose monitoring can assist in the diagnosis. During the 31st week of pregnancy, it is important to follow the doctor’s instructions to have regular checkups and to keep a strict fetal movement count to self-evaluate the condition of the fetus in the womb. Moderate physical activity is also prescribed. For pregnant women with diabetes mellitus, strict control of blood glucose should be carried out under the guidance of the doctor to avoid the occurrence of macrosomia. In the case of gestational hypertension, the blood pressure should be actively controlled and the growth and development of the fetus should be monitored.