If an infant is still unstable at eight months of age, it is an abnormal phenomenon, because a normal infant is already sitting steadily six months after birth, and if an infant is still unstable at eight months of age, it is obviously a developmental delay. Secondly, when the infant suffers from a disease, such as congenital hypothyroidism, the infant is not given thyroxine tablets in time to replace the treatment, which will cause a developmental delay and the infant’s intelligence will be greatly affected.