Calculator Inputs
Example Data Table
| Case | Sex | Age | Weight | Length | Head Size | Likely Review |
|---|---|---|---|---|---|---|
| Preterm A | Male | 29 weeks | 1200 g | 38 cm | 27 cm | Compare all percentiles together. |
| Preterm B | Female | 32 weeks | 1500 g | 40 cm | 29 cm | Watch weight-to-length balance. |
| Term Review | Male | 40 weeks | 3400 g | 50 cm | 35 cm | Usually near central bands. |
Formula Used
Gestational age: weeks + days ÷ 7.
BMI: weight in kilograms ÷ length in meters squared.
Z score: entered measurement − reference median, divided by reference standard deviation.
Percentile: normal distribution area from the z score × 100.
Target weight: reference median + target z score × reference standard deviation.
Weight gain: current weight − previous weight, divided by elapsed days.
This file uses editable reference arrays and smooth interpolation. For clinical publication, update the arrays with verified local or official chart values.
How to Use This Calculator
Choose the infant sex first. Enter completed gestational weeks and extra days. Add weight, length, and head circumference. Select the correct units before calculating. Add a previous weight when you want a daily gain estimate. Choose a target percentile if you want a reference weight goal. Press the calculate button. The result appears above the form and below the header. Use CSV or PDF buttons to save the same calculation.
Olsen Growth Chart Guide
Why Growth Percentiles Matter
Preterm infants need careful growth review. Their size changes fast. A single number rarely tells the full story. Weight, length, and head circumference should be reviewed together. The Olsen style chart helps compare a newborn with babies of similar gestational age and sex. This gives a clearer screening view.
Understanding the Main Outputs
The weight percentile shows where the infant sits among reference newborns. A value below the tenth percentile may support small-for-gestational-age review. A value above the ninetieth percentile may support large-for-gestational-age review. These labels are screening bands. They are not a diagnosis. The clinical situation still matters.
Using Length and Head Size
Length helps explain body proportion. Head circumference helps review brain and skull growth. A baby may have a low weight percentile but a better head percentile. That pattern can have many causes. Measurement error is also common. Always confirm tape position, scale accuracy, and gestational age.
BMI and Proportion Review
BMI is useful when weight and length need joint review. It can show whether weight is low or high for body length. This calculator estimates BMI percentile with the same internal reference method. It should be used as a supportive clue. It should not replace neonatal assessment.
Practical Use in Care Teams
Exported CSV files help with records. PDF summaries are useful for quick case review. Keep notes short and factual. Compare serial values over time. A stable trend can be more useful than one isolated percentile. Discuss unexpected values with a trained clinician before making nutrition or treatment changes.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates preterm growth percentiles for weight, length, head circumference, and BMI. It also gives z scores, screening bands, target weight, and optional daily weight gain.
2. Is this a diagnosis tool?
No. It is an educational screening calculator. A clinician should review the infant, measurements, gestational age, feeding history, and local growth policy before making decisions.
3. What does SGA mean?
SGA means small for gestational age. In this calculator, it appears when estimated weight is below the tenth percentile screening band.
4. What does AGA mean?
AGA means appropriate for gestational age. It usually refers to weight between the tenth and ninetieth percentile bands for the entered sex and age.
5. What does LGA mean?
LGA means large for gestational age. In this calculator, it appears when estimated weight is above the ninetieth percentile screening band.
6. Why enter length and head circumference?
They add context. Weight alone can miss proportion issues. Length and head size help compare body growth, nutrition pattern, and measurement consistency.
7. Why does the tool calculate BMI?
BMI links weight with length. It can support proportional growth review, especially when weight percentile and length percentile do not align well.
8. Can I export the result?
Yes. Use the CSV button for spreadsheet records. Use the PDF button for a simple printable summary of the entered values and calculated results.