Humerus length is an indicator of fetal development measured by ultrasound during pregnancy, which reflects the length of the fetal upper arm humerus. The humerus length increases with the increase of gestational weeks, and together with the fetal biparietal diameter, head circumference and abdominal circumference, it can be used to comprehensively assess whether the fetal growth and development are normal, so as to determine the fetal weight and help in prenatal screening and the choice of delivery method. The common causes of abnormal humerus length include measurement error, congenital long or short humerus, nutritional factors, abnormal fetal development, etc. 1.Measurement error: if the fetal position changes during the examination, improper operation of the examination, or abnormal instrumentation, it may lead to deviation in measurement and thus abnormal humerus, which is generally not a cause for concern; 2.Congenital long or short humerus: some fetuses The humerus may be long or short due to genetic reasons, and the fetus with serious humeral abnormalities should be treated under the guidance of a doctor; 3, nutritional factors: too much nutrition may lead to a long humerus, and too little nutrition may lead to a short humerus, and such patients should pay attention to a reasonable diet with nutrition, to avoid excessive nutrition or lack of nutrition, and can reduce or add calcium-containing substances under the guidance of a doctor according to their own situation; 4, fetal development 4, abnormal fetal development: there may also be fetal dysplasia resulting in a long or short humerus, if the pregnant woman is also accompanied by irregular abdominal pain and other symptoms, should promptly go to the hospital for related treatment. If the humerus length is abnormal, it should be combined with other examination results such as femur length and 4D ultrasound to make a comprehensive assessment. If it indicates that the fetus has serious overweight, underweight or developmental malformation, relevant treatment should be carried out under the guidance of the doctor, and if necessary, pregnancy should be stopped in time.