GP FAQ head circumference

Head circumference (HC) and weight do not have to track the same centile in infants. HC relates much more to parental head size than weight.

When assessing a baby, ensure that the HC was measured correctly, it is very easy to get multiple different readings and the maximal measurement should be determined. It is important to take serial measurements of head circumference if there is any concern about growth.

In an infant with a large head, look for signs of raised intracranial pressure e.g. sunset eyes, distended scalp veins, the ‘cracked pot’ sound on percussion of the skull and optic disc swelling on fundoscopy.  Other factors that would also necessitate an urgent review include history of central nervous system trauma or infection, neurodevelopmental abnormalities and syndromic features.

The posterior and anterior fontanelles fuse at 1-2 month and 9-18 months respectively (1% of normal babies have a closed anterior fontanelle by 3 months).

The size of the fontanelle can vary greatly and the most important thing is that it is patent and that there is evidence of increasing head circumference along the centile. If you continue to monitor the HC and there are concerns regarding early closure of a fontanelle or not following the HC centiles then a referral to secondary care is warranted.


Boragina, M, Cohen E. An infant with the setting sun phenomenon.

Neonate with marked macrocephaly due to hydrocephalus. UptoDate.

Measurement of head circumference. UpToDate