Whether a head is 'abnormally' large depends on the growth chart used
The Fifteen-minute consultation on the infant with a large head just published on line (1) has one major weakness: no mention of which chart the child's head is compared to. Comparison with representative Belgian, Norwegian (2) and British data (3) has shown that European infants' heads appear large compared to the WHO standards. We have undertaken further analyses of the data from the Southampton Women's Survey used for our previous paper (3) and these suggest that, out of 1731 healthy infants aged 6 months, 3.3% have a head circumference (HC) above the WHO 99.6th centile and half of these (1.8% of all infants) will also have crossed 2 or more centile spaces upwards since birth. Reassuringly, between 6 and 12 months there was much less centile crossing and only 5 infants (0.3% of all infants) move further upwards by more than the equivalent of one centile space (0.67SD). It is probably these latter children who should be investigated further.
If compared to the previous UK 1990 growth chart only around 0.5% of children will have a head circumference above the 99.6th, but it should be born in mind that compared to the UK 1990 UK more infants' heads appear small. After the age of 6 months between 5-8% of children have heads below the UK1990 2nd centile (3) and our further analyses of the latter data3 suggest that by 6 months of age 17% of healthy infants will have crossed 2 or more centile spaces downwards compared to the UK 1990 reference.
So the growth chart you choose makes a huge difference: make sure you know which one is being referred to!
(1) Seal A. Fifteen-minute consultation on the infant with a large head. Arch Dis Child Educ Pract Ed 2013. (2) Juliusson PB, Roelants M, Hoppenbrouwers K, Hauspie R, Bjerknes R. Growth of Belgian and Norwegian children compared to the WHO growth standards: prevalence below -2 and above +2 SD and the effect of breastfeeding. Arch Dis Child 2011; 96(10):916-921. (3) Wright CM, Inskip HM, Godfrey K, Williams AF, Ong KK. Monitoring head size and growth using the new UK-WHO growth standard. Arch Dis Child 2011; 96(4):386-388.
Conflict of Interest:
I am academic lead for the RCPCH growth chart group that published the new UK-wHO growth charts