The ultrasound sheet is read to estimate the size of the baby by monitoring the biparietal diameter, head circumference, chest circumference and femur length of the fetus. There are many specific calculations for estimating the size of the fetus by ultrasound, such as fetal weight (g) = 747.42 x humerus length – 2232.56 (in cm) or fetal weight (g) = 260.69 x head circumference – 4973.72 (in cm) or fetal weight (g) = 171.48 x abdominal circumference – 2686.60 (in cm), and usually in the mid to late stages of pregnancy, the ultrasound The doctor will write the weight value in the report. Because the condition of each pregnant woman is different, the fetal weight calculated by ultrasound data has some errors, so it can only be used as a reference for the development of the fetus.The value measured by ultrasound can also be compared with the gestational week to check the development of the fetus. If the fetus is too large or too small on ultrasound, it is necessary to actively consult a doctor for examination, clarification of the cause of the disease and treatment of the original disease.