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Olsen Preterm Length-for-Age Growth Chart (0-24 Months)

Plot a preterm infant's length against the Olsen growth curves for ages 0-24 months. Half-month interval data points provide high-precision tracking during early growth.

LMS Method: Z = ((X/M)^L - 1) / (L x S)

How It Works

This calculator uses the Olsen preterm growth curves for monitoring length in infants from birth to 24 months. The Olsen charts are designed specifically for infants born prematurely, providing a more appropriate reference than standard WHO or CDC charts during the catch-up growth period. The data uses half-month intervals for high-resolution tracking. The LMS method computes Z-scores and percentiles.

Example Problem

A premature infant (born at 28 weeks) is now 6 months chronological age and measures 58 cm in length. What is the length-for-age percentile on the Olsen chart?

  1. Enter the infant's date of birth and measurement date.
  2. Select the gender.
  3. Enter 58 cm for length.
  4. The calculator computes the age and finds the Olsen LMS parameters.
  5. Result: the Olsen percentile is displayed, providing a preterm-specific assessment.

Key Concepts

Preterm infants have different growth trajectories than full-term infants and often experience catch-up growth during the first 2-3 years. The Olsen charts provide preterm-specific reference data. Corrected age (from the due date, not the birth date) should be used when assessing preterm growth until about 24 months. WHO charts represent standards for healthy term breastfed infants and may not be appropriate for preterm growth assessment during the catch-up period.

Applications

  • Growth monitoring for preterm infants during the first 2 years
  • Tracking catch-up growth after premature birth
  • NICU follow-up clinic assessments
  • Evaluating nutritional interventions for preterm infants
  • Research on preterm infant growth outcomes

Common Mistakes

  • Not using corrected age for preterm infants — corrected age should be used until about 24 months
  • Using standard WHO or CDC length charts without considering the preterm growth trajectory
  • Measuring standing height instead of recumbent length for infants
  • Not recognizing that catch-up growth is expected and normal in preterm infants
  • Comparing Olsen percentiles directly to WHO or CDC percentiles

Frequently Asked Questions

What age range does this calculator cover?

This calculator covers ages from birth to 24 months, with data at half-month intervals for high-precision tracking during early growth.

How is this different from WHO length-for-age charts?

The Olsen preterm charts are designed specifically for infants born prematurely. WHO charts represent growth standards for healthy breastfed term infants. For preterm infants, the Olsen charts may provide a more appropriate comparison.

Should I use cm or inches?

You can use either unit. The calculator converts automatically. For clinical accuracy, use the exact measurement from your healthcare provider.

Reference: Olsen IE, et al. New intrauterine growth curves based on United States data. Pediatrics. 2010;125(2):e214-e224.

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