Abdominal circumference at 31 weeks of pregnancy in 82-95cm is more normal, according to the individual size of pregnant women may have 1-2cm deviation. Generally from about 16 weeks of pregnancy to measure the abdominal circumference, standing or lying down to the navel prevail, horizontal around the abdomen for 1 week measured data for the abdominal circumference, under normal circumstances, the abdominal circumference of the average weekly growth of 0.8cm, 20-24 weeks of pregnancy when the fastest growth, 34 weeks after the slowdown in the growth rate, if the growth is too fast or too slow, should be promptly consulted for medical examination. The size of the abdominal circumference varies from person to person, physiological and pathological factors can lead to large or small abdominal circumference. Physiologically, obese or thin body type pregnant women will be large or small waist; some pregnant women in the post-pregnancy appetite increase, rapid weight growth, with the change in body size of the abdominal circumference will also be rapid changes; the fetus is larger or smaller will also affect the size of the abdominal circumference. Pathologically, when the abdominal circumference is large, consider gigantic children, gravida, excessive amniotic fluid, pregnancy combined with abdominal tumors, and so on. When pregnant women are overnourished, they are prone to have huge babies, in which case the abdominal circumference is relatively large and difficult to deliver in the later stage; excessive amniotic fluid makes the abdomen enlarge and the abdominal circumference become larger, in which case pregnant women are prone to have difficulty in breathing, edema of the lower limbs and perineum, and preterm labor, etc.; if the abdominal circumference grows too rapidly, we can consider gravidarium; and tumors of the abdomen in combination with pregnancy also lead to the abdominal circumference to be large. When the abdominal circumference is small, it is considered to be intrauterine growth retardation, in which the fetus is less tolerant to hypoxia, and it is more difficult to give birth in the later stage, and it will also increase the risk of coronary heart disease and hypertension in the adult. In conclusion, when the abdominal circumference deviates from the normal value or changes rapidly, you should consult a doctor for observation and treatment in order to prepare for the later stage of labor.