The belly of a 20-week pregnant woman varies from person to person. Under normal circumstances, the abdominal circumference of the fetus in this gestation week is between 13.1cm-16.5cm, the head circumference is between 15.2-18.6cm, the uterine fundus is basically at 1 transverse finger below the umbilicus, and the lower abdominal expansion is dominant, and there is no standardized criterion because every pregnant woman’s body shape is different. Generally speaking, we measure the biparietal diameter, head circumference, abdominal circumference, femur length and amniotic fluid volume of the fetus by ultrasound to determine its growth and development, if the indicators are in the normal range, that is to say, the development of the fetus is normal; and the size of the pregnant woman’s stomach in addition to the fetus, but also its own body weight and abdominal fat is related to the fetus, can not represent the development of the fetus. During pregnancy, pregnant women are advised to control their diet and maintain their weight growth scientifically, as overweight or underweight is not conducive to the growth and development of the fetus.