The ultrasound shows that sometimes the abdominal circumference is not long and sometimes the biparietal diameter and femur length are not long, which may be related to the abnormal development of the fetus, the position of the fetus during the measurement and the doctor’s measurement technique. 1. Abnormal development of the fetus: the fetus continues to develop throughout the pregnancy, and there are reference ranges for abdominal circumference, biparietal diameter, and femur length in the corresponding gestational weeks, which can be used to effectively judge the growth and development of the fetus. Fetal development process is affected by genes, maternal function and other factors, there may be relevant meridian not long. 2. The position of the fetus during measurement: As the position of the fetus may be different during each ultrasound examination, it may be affected during the measurement process, sometimes the abdominal circumference is not long and sometimes the biparietal diameter and femur are not long. 3. The doctor’s measurement method: When each doctor conducts ultrasound examination, the measurement method and the instruments used may be different, thus affecting the data of ultrasound examination. Sometimes the abdominal circumference is not long and sometimes the biparietal diameter and femur are not long. If the ultrasound measurement of abdominal circumference, biparietal diameter and femur length do not correspond to the week of pregnancy, you should go to the hospital for consultation. Ask a professional obstetrician to evaluate the fetal development.