What is microcephaly?

Microcephaly is defined as head circumference more than 2 standard deviations (SD) below the mean for age and sex, corresponding to below the 3rd percentile. Severe microcephaly is >3 SD below mean.

What causes macrocephaly?

Macrocephaly (head circumference >97th percentile) may be caused by familial large head, hydrocephalus, megalencephaly, storage diseases, or subdural collections. Familial macrocephaly is often benign.

How often should head circumference be measured?

Head circumference should be measured at every well-child visit from birth through 24 months, and at 3-year and 4-year visits. Serial measurements plotted on growth charts are more informative than a single measurement.

Head Circumference Percentile

Determine head circumference percentile by age and sex using CDC growth charts. Microcephaly <3rd percentile, macrocephaly >97th percentile.

Use the full interactive calculator below, or

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Frequently Asked Questions

What is microcephaly?

What causes macrocephaly?

How often should head circumference be measured?