Head circumference is an important sign of brain tissue and cranial development, and the head circumference standards in different periods include the following: 1. The measurement of head circumference during childhood often reflects the development of brain tissue and skull, and both large and small head circumference indicate the possibility of intracranial abnormalities, especially around 2 years of age. The measurement of head circumference is an important reference for the intracranial condition of the child. Oversized head circumference is mainly seen in hydrocephalus and rickets. Small head circumference often indicates the possibility of microcephaly and should be a cause for concern.