The left arm and leg of a 3-month-old baby is not as flexible as the right side is usually normal, but we should pay attention to whether there is any improvement or aggravation, and if necessary, we can improve the X-ray and other tests to clarify the diagnosis. Usually the left side of the arms and legs of 3-month-old babies tend to be less flexible than the right side, but it is not obvious that careful observation is needed to find out. The main reason for this is that most babies are right-handed, resulting in the right side of the arms and legs being more flexible than the left side, which is a normal phenomenon. But also need to be vigilant about the possibility of disease, such as clavicle fracture, generally speaking, during the newborn period, when passing through the birth canal will be squeezed, can lead to the appearance of clavicle fracture, this situation is prone to the left shoulder joint activities significantly reduced, manifested in the left arm is not as flexible as the right side. In this case, you can consult a doctor in time and improve the X-ray to make a clear diagnosis. If there is no fracture, if necessary, training can be carried out, some babies can be improved after training. Most 3-month-old babies left arm and leg without the right side of the flexible is a normal phenomenon, if you are not sure you can go to a regular hospital pediatrics, and under the guidance of the doctor for a physical examination, if necessary, improve the X-ray and other tests to make a clear diagnosis, and comply with the doctor’s instructions for targeted treatment and training.