Preterm Head Circumference-for-Age Percentile Calculator (Olsen)

How Preterm Head Circumference-for-Age Percentiles Work

This calculator uses growth reference curves to assess head circumference-for-age for preterm infants from birth through 24 months. Head circumference is an important indicator of brain growth, particularly in premature infants.

The calculator uses the LMS method with age-specific parameters at half-month intervals, providing precise tracking of head growth during the critical period of brain development.

Why Head Circumference Matters for Preterm Infants

Head circumference is one of the most important growth parameters for premature infants because it reflects brain growth. Preterm infants may show different head growth patterns compared to full-term infants, making preterm-specific growth charts essential for accurate assessment.

• Rapid head growth is expected in the first months after birth
• Below the 3rd percentile (microcephaly) may warrant further evaluation
• Above the 97th percentile (macrocephaly) may also need assessment
• Consistent tracking over time is more valuable than a single measurement

Example Calculation

A boy at birth with a head circumference of 35.81 cm would be at approximately the 50th percentile on the Olsen chart, since this is the median value at that age.

Frequently Asked Questions

What age range does this calculator cover?

This calculator covers ages from birth to 24 months, with half-month interval data points for high-resolution tracking.

How should I measure head circumference?

Head circumference should be measured using a flexible, non-stretchable tape measure placed around the largest part of the head (occipitofrontal circumference). The measurement should be taken by a healthcare professional for accuracy.

Are these the same charts used in the NICU?

Many NICUs use the Olsen or similar preterm growth charts for monitoring head growth. Always consult with your healthcare provider for clinical interpretation of results.