Part of the vital signs drill pediatricians employ during regular well-child checkups in the first two years of life is measuring a baby’s/toddler’s head circumference. The brain undergoes its greatest growth during this time, so it makes sense to track the growth of the skull as its bones fuse together. Pediatricians have always thought that the actual size of a child’s head is less important than that it grows consistently, along lines of percentiles on standard growth charts. Inconsistent measurements showing head circumference growing too fast, or not fast enough, are viewed by pediatricians as red flags of some underlying, neurodevelopment disorders. A new study, published last month in Pediatrics, turns that idea on its head: Inconsistencies in head circumference measurements are almost always due to measurement error and are not indicative of underlying brain abnormalities.

The British study involved more than 10,000 children and it found that measurements crossing percentiles on head circumference growth charts during the first two years hardly ever uncovered neurodevelopmental or neurocognitive pathology. While a rapidly growing head circumference in very young babies can signify the very serious-but-rare condition of hydrocephalus, most of the time it only leads to costly and anxiety-causing diagnostic tests which ultimately prove negative. The researchers conclude:

When HC is measured, clinicians and parents can be reassured that the majority of children with small heads will have no underlying pathology and that the commonest explanation for an increase or decrease in head centile is measurement error. Given the great variability in HC measurement, the more often a child’s head is measured, the more often spurious extreme or shifting head size will be seen…

…We suggest an HC measurement in the first 2–5 days after birth, but not in the first 48 hours to allow time for resolution of molding during birth and once more before the age of 6 months. Otherwise, HC should not be routinely measured as part of a complete physical examination.


This study once again highlights the importance of detailed developmental histories and thorough physical examinations by pediatricians and other pediatric medical specialists who are trained to recognize what is abnormal, and normal, in children. That always beats chasing numbers on a growth chart which tend to be, at best, subjective.