Fetal femur length of 4.5cm at 30 weeks of pregnancy may have deformity, or it may be caused by heredity or malnutrition. First of all, amniocentesis can be used to detect malformations, and secondly, more nutrition can be added to promote bone development. The normal range of femur length in 30 weeks of pregnancy is 5cm~6cm, 4.5cm is relatively short, which may be caused by deformity, heredity or malnutrition. At this time, you can check for malformations through amniocentesis, and if there is no abnormality, you can take more calcium tablets and strengthen nutrition. At the same time, other indicators should also be observed to see if they are normal. If the femur is only short and slightly smaller than the size of a child of the same age, the development of the fetus is usually not seriously affected. During the preparation and pregnancy, you should strengthen nutrition, eat a balanced diet, and take vitamin D and calcium tablets as appropriate. Meanwhile, during pregnancy, you should take obstetric checkups on time and pay attention to the growth and development of the fetus at all times.