Fetal ultrasound can be performed to measure the length of the fetal femur to see whether the fetus has long or short legs. Fetal ultrasound examination during pregnancy can understand the growth and development of the fetus, whether there is any organ and tissue development deformity, etc. It is one of the very important examination items for eugenics. Generally in the middle and late stages of pregnancy, the fetal femur length can be roughly measured by ultrasound, and compared with the reference range of gestational weeks to determine whether the fetal femur length is normal. Fetal femur length is an indicator used to determine fetal development during ultrasound examination, and it gradually increases with the increase of gestational weeks. Generally speaking, as long as the fetal ultrasound results are basically in line with the reference range of gestational weeks, it means that the fetus is developing normally and there is no need to worry. If the femur length of the fetus is significantly lower than the lower limit of the reference value of the gestational week, it is considered that the fetus has delayed development or there is a genetic disease, and comprehensive examination is needed to analyze the cause.