Results:
Head Circumference for Age Percentile Interpretation
| Percentile < 3: | Microcephaly |
| Percentile >= 3 and < 97: | Normal head circumference |
| Percentile >= 97: | Macrocephaly |
- Microcephaly is a Head Circumference greater than two standard deviations below the mean.
- Macrocephaly is a Head Circumference greater than two standard deviations above the mean.
- At the extremes (>97th percentile or <3rd percentile), small differences in percentiles represent clinically important differences in head circumference. At these extremes, the z-score is a more precise reflection of how far the measurement deviates from the mean, and is a useful tool for tracking changes.
Examples
| Z-score | Percentile equivalent |
| - 3.0 | 0.3 |
| - 2.0 | 2.5 |
| + 2.0 | 97.5 |
| + 3.0 | 99.7 |
- Percentile conversion from Z-Score is done by table look-up in the standard Normal Table. Percentiles are provided for Z Scores between -3.09 and 3.09. Values beyond these extremes return percentiles of 0.1 and 99.9 respectively.
- LMS Parameters for Girls: Head Circumference for Age. National health and nutrition survey (NHANES), CDC/National Center for Health Statistics.
- LMS Parameters for Boys: Head Circumference for Age. National health and nutrition survey (NHANES), CDC/National Center for Health Statistics.