Head circumference is a measurement of a child’s head around its largest area -- it measures the distance from above the eyebrows and ears and around the back of the head.
During routine check-ups, the distance is measured in centimeters and compared with previous measurements; normal ranges are based on sex and age (weeks, months).
Measurement of the head circumference is an important part of routine well baby care. Through the years, doctors have obtained values for normal growth rates of infants and young children's heads. During the well baby exam, a deviation from the expected normal head growth may alert the doctor of a possible problem.
For example, a head that is larger than normal or whose size is increasing faster than normal may be a sign of increased intracranial pressure , which can be caused by any number or problems including water on the brain (hydrocephalus).
An exceptionally small head size (called microcephaly ) or very slow growth rate may be a sign that the brain is not developing properly.
Kimmel SR, Ratliff-Schaub K. Growth and development. In: Rakel RE, ed. Textbook of Family Medicine. 7th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 31.