The fetus is an amazing little life, and in a total of 40 weeks, the baby will grow and develop rapidly until the melon is ripe. During maternity checkups, mothers ask the doctor if the baby is growing well and is it normal? Well, from the medical point of view, there are some indicators to judge, and femur length is one of them. The femur is the largest long bone in the body, referring to the thigh bone, and as the name implies, the femur length is also the length of the thigh bone. Femur length reflects the degree of development of the baby’s long bones and can also be used to estimate the weight of the fetus. In our hospital, the femur length is measured at every ultrasound starting from the middle of pregnancy. Some mothers often ask, “Is it a problem if the ultrasound says my baby’s legs are short? In most cases, mothers should not be too nervous about the data, especially in the middle and late stages, the difference in fetal position and the difference in the operation of different doctors can cause errors, sometimes even fluctuations can be very large, after 30 weeks, there can be errors in the upper and lower two weeks, and the standard values we use are mostly European and American standards, so there is no need to be too nervous when you see a discrepancy between the reported results and the normal values. And genetics is also a very important factor, if the parents are not tall, the baby may also have short legs. However, if the baby’s femur length is significantly shorter than normal, or if it is combined with other problems or even deformities, then the baby has a higher chance of having problems and needs to be taken seriously. The common causes are as follows: (1) lethal dwarfism: In addition to severe leg shortening, you may also see curved long bones, large head, prominent forehead, excessive amniotic fluid, clover-shaped head, etc., and the baby will not survive after birth; (2) chondrodysplasia: It is the most common type of hereditary dwarfism, mostly non-lethal, with slowed long bone development from 21-27 weeks, imbalance of femur length/biparietal diameter ratio, accompanied by (3) Osteogenesis imperfecta: also known as brittle bone disease, brittle bone – blue sclera – deafness syndrome, commonly known as “porcelain doll” disease, divided into types I-IV, manifesting as increased brittleness of the bones, the long bones of the limbs are significantly short, bent and fractured, accompanied by the bones of the skull, spine and thorax. (4) Combination of other multiple anomalies: may indicate chromosomal anomaly syndrome, and if necessary, amniocentesis or cord blood puncture is required to check fetal chromosomes. In addition to giving the anxious mother a clear diagnosis, we can also give professional advice on whether further chromosomal examination is needed, whether the baby needs to be induced, whether there are problems after birth, whether the baby can be conceived again, and what to look for in the next pregnancy. What to look for in the next pregnancy. In addition, we have also seen a mother of a “porcelain doll” who came all the way to our hospital in a wheelchair and found that her baby had inherited the same disease from her mother. Finally, I wish all pregnant mothers a healthy baby with strong bones!