How to Measure Parental Head Circumference
To measure a parent's head circumference for assessing familial macrocephaly, use a firm non-stretchable measuring tape positioned just above the supraorbital ridges anteriorly and around the occiput posteriorly at the point of maximum circumference, with the parent's head upright and straight. 1, 2
Equipment Required
- Firm, non-stretchable measuring tape (cloth or paper tape measures are preferred over elastic types) 1, 2
- Pen and paper for recording measurements 1
Measurement Technique
Positioning
- Have the parent sit or stand with their head in an upright position, looking straight ahead 2, 3
- The axis of vision should be horizontal, with the parent looking forward 1
Tape Placement
- Locate the supraorbital ridges (the bony prominences above the eyes) anteriorly 1, 2
- Locate the occipital bone (the most prominent point at the back of the head) posteriorly 1, 2
- Apply the tape firmly around the head just above the supraorbital ridges at the same level on both sides, wrapping around to the occiput 1, 2
- Apply sufficient tension to compress the hair against the skull without causing discomfort 2
- Ensure the tape is positioned to obtain the maximum circumference 2, 3
Recording
- Read the measurement to the nearest 0.1 cm 1, 2
- Perform multiple measurements (ideally 2-3) and use the largest value, as this represents the true maximum circumference 3
Clinical Context for Familial Macrocephaly Assessment
When to Measure Parental Head Circumference
- Measure both parents' head circumferences when a child presents with macrocephaly (head circumference >97th percentile or +2 SD above the mean) 4, 5
- Mild macrocephaly ≤2.5 SD carries a good prognosis, especially when one parent has macrocephaly and normal development 4
Interpretation
- If one or both parents have macrocephaly with normal development, this strongly suggests benign familial macrocephaly in the child 4, 6
- Cases where parental head circumferences are normal are more concerning and warrant further investigation including neurosonogram, fetal MRI, and genetic testing 4
- Benign familial macrocephaly is an autosomal dominant disorder characterized by large absolute head circumference with proportional rather than excessive growth rate 6
Common Pitfalls to Avoid
- Avoid using elastic or stretchable measuring tapes, as these produce inconsistent measurements 2, 7
- Do not measure over bulky hairstyles without compressing the hair adequately against the skull 7
- Ensure the tape is level on both sides of the head and not tilted 1
- Do not rely on a single measurement—serial measurements or multiple readings at one time improve accuracy 2, 3