Head circumference reflects the level of development of the brain and skull. Under normal circumstances, the head circumference of a 3-year-old baby is 45.7-53.5cm for boys, with an average of 49.6cm, and 44.8-52.6cm for girls, with an average of 48.5cm. The average head circumference of newborn babies is 34cm, the average head circumference at the age of 1 year is about 46cm, at the age of 2 years, the head circumference is about 48cm, at the age of 3 years, the head circumference is about 50cm. if the baby’s head is small and pointed, and the forehead is narrow and small, it may be a cerebellar deformity, and at this time the child’s intellect and physical strength will be affected. If the baby’s fontanel is full and the forehead is wide, it suggests that the head circumference is large, which is often caused by certain diseases, such as hydrocephalus and brain tumors. Therefore, when you find that your baby’s head circumference is large or small, you should consult a pediatrician or neurosurgeon in a timely manner to clarify the cause of the disease and take targeted treatment.