An ingrown thumb is not necessarily a sign of slow brain development, but may also be a physiologic phenomenon. It is recommended that the degree of development be evaluated under the guidance of a medical professional. 1. Due to the dominance of flexor muscles, small babies show the phenomenon of clenching fists and withholding their thumbs for a period of time after birth. The gripping reflex shown by small babies may be the withholding of thumbs, which belongs to normal physiological reflexes of babies, and is not a manifestation of slow cerebral development. 2. If the baby has slow brain development or suffers from cerebral palsy and other diseases, the phenomenon of thumb inward fastening will continue to appear. Therefore, when the baby still shows thumb inward fastening after 4~6 months, it is necessary to be highly vigilant, and bring the baby to the pediatrics or rehabilitation department of the hospital in time, so as to clarify the cause of the disease in time, and give the appropriate intervention and treatment according to the cause of the disease. It is recommended to go to the hospital and be evaluated by a medical professional to determine whether the thumb inversion is a result of slow brain development.