Early or late closure of a baby’s fontanel is problematic. The closure of a baby’s fontanel at 5-6 months of age is considered early closure and may be the cause of poor brain development in babies. The fontanel normally closes between 12 and 18 months after birth, and closes at the latest at 2 years of age. 1. Brain dysplasia: the premature closure of the fontanel should be measured to determine the size of the head circumference, if the head circumference is smaller than normal, it may be congenital cranial and cerebral dysplasia; some babies will also have microcephaly, resulting in retarded or low intellectual development. 2. Hypothyroidism: If the closure of the fontanel is delayed, it may be related to hypothyroidism and increased intracranial pressure, and it is recommended to actively seek medical attention. It is not normal for a baby’s fontanel to close too early or too late. If you find that your baby’s fontanel is abnormal, it is recommended that you consult a doctor in time.