Nutritional assessment of preterm infants using corrected age
Enter sex, gestational weeks at birth, weight, length, head circumference and the dates of birth and assessment. You get the corrected age and the nutritional, growth and head circumference status against the Chilean intrauterine curves or the WHO standards.
For: Babies born before 37 weeks, up to 24 months of corrected age (born before 32 weeks) or 12 months (32 to 36 weeks). Free, no sign-up. Everything is worked out in your browser and nothing is stored.
How corrected age is worked out
The calculator counts the days of life between the date of birth and the date of assessment and subtracts the days that were missing to reach 40 weeks at birth:
days of corrected age = days of life − (40 − gestational weeks) × 7
If the result is 0 or negative, the baby has not yet reached 40 corrected weeks: the corrected weeks are 40 plus the corrected days divided by 7 (rounded), and the assessment uses the intrauterine curves. If it is positive, the corrected age in months and days is worked out and the WHO standards for that age are used.
| Gestational weeks at birth | Classification in the calculator | Age corrected up to |
|---|---|---|
| Under 32 | Extremely preterm | 24 months |
| 32 and 33 | Moderately preterm | 12 months |
| 34 to 36 | Late preterm | 12 months |
| 37 or more | Not assessed as preterm | — |
Up to 40 weeks: intrauterine curves
The measurements are compared with the percentiles for the corrected week (the tables run from 24 to 42 weeks; below 24 corrected weeks there is no data). Weight is entered in kilograms, but at this stage a value of 10 or more is read as grams. The ponderal index is weight (g) / length (cm)³ × 100.
| Measurement | Percentile for the week | Result |
|---|---|---|
| Weight | Below p3 / from p3 and below p10 | Small for gestational age: severe SGA / SGA |
| Weight | p10 to p90 | Appropriate for gestational age (AGA) |
| Weight | Above p90 | Large for gestational age (LGA) |
| Ponderal index | Below p10 / p10 to p90 / above p90 | Wasted asymmetric newborn / normal symmetric newborn / overweight asymmetric newborn |
| Length | p10 or below | Intrauterine growth restriction (IUGR), instead of the ponderal index result |
| Head circumference | Below p10 / from p10 and below p90 / p90 or above | Suspected microcephaly / normal / suspected macrocephaly |
The date on which the baby reaches 40 corrected weeks is also shown, along with the difference between each measurement and the mean for that week.
After 40 weeks: WHO standards with corrected age
Length must be between 45 and 110 cm. SD: standard deviations for the corrected age in months.
| Indicator | Criterion | Result |
|---|---|---|
| Weight for age | Below −2 SD / from −2 SD and below −1 SD | Undernutrition / at risk of undernutrition |
| Weight for age | From −1 SD and below +1 SD / +1 SD or above | Normal / normal * (use professional judgement) |
| Weight for length | From +1 SD and below +2 SD / +2 SD or above | Overweight / obesity (replaces the weight-for-age result) |
| Length for age | Below −2 SD / from −2 SD | Stunted growth / normal growth |
| Head circumference for age | −2 SD or below / between −2 and +2 SD / +2 SD or above | Suspected microcephaly / normal / suspected macrocephaly |
The acceptable range shown runs from −1 to +1 SD for weight and length, and from −2 to +2 SD for head circumference.
Charts and report
While the assessment is intrauterine, the four curves from 24 to 42 weeks are drawn (weight, length, head circumference and ponderal index) with the patient's point. The point sits at the week of corrected age, which is the week used for the classification. The old site placed it at the gestational week at birth, so the chart did not match the result shown on the same page; that has been fixed here. Each chart has a table with the same values underneath.
With a result, a «Download report» button appears: a PDF built in your browser with the data entered, the result, the reference table, the charts and the source. You can add an optional reference for your own records, which only goes into that PDF.
Frequently asked questions
How is a preterm infant's corrected age calculated?
The weeks that were missing to reach 40 at birth, multiplied by 7, are subtracted from the days of life. For example, a baby born at 30 weeks who is 100 days old has 100 − (40 − 30) × 7 = 30 days of corrected age. If the result is 0 or negative, the baby has not yet reached 40 corrected weeks.
Up to what age is age corrected?
Up to 24 months of corrected age for babies born before 32 weeks, and up to 12 months for those born at 32 to 36 weeks. Past that limit the calculator does not assess and points to the children's module of EvaNu or EvaNuWeb. From 37 weeks a baby is not considered preterm.
Which curves does it use?
While the corrected age is under 40 weeks, the Chilean national intrauterine growth curves (Alarcón-Pittaluga), with weekly percentiles for weight, length, head circumference and ponderal index from 24 to 42 weeks. After 40 weeks, the WHO growth standards using the corrected age in months.
What is the ponderal index?
It is the weight in grams divided by the length in centimetres cubed, multiplied by 100. Below the 10th percentile for that week it indicates a wasted asymmetric newborn; above the 90th, an overweight asymmetric newborn; between the two, a symmetric newborn. If length is at or below the 10th percentile, the result is intrauterine growth restriction (IUGR).
Is weight entered in kilograms or grams?
In kilograms, with a comma or full stop as the decimal mark (1.85, for example). Only during the intrauterine stage is a value of 10 or more read as grams. Length and head circumference are in centimetres; with a positive corrected age, length must be between 45 and 110 cm.
Which week is the patient's point plotted at on the charts?
At the week of corrected age, the same one the result is classified against. The old site plotted it at the gestational week at birth, so the point on the chart did not match the result shown on the same page: that has been fixed. The charts appear while the assessment is intrauterine; past 40 corrected weeks the WHO standards are used and the intrauterine curves no longer apply.
Can I download a report?
Yes. When there is a result, a «Download report» button appears that builds a PDF in your browser with the data entered, the result and its classification, the reference table used, the charts and the source. Nothing is sent or stored. You can type an optional reference (a case number, for instance) that only goes into that PDF; do not enter names or ID numbers.
Is the data I enter stored?
No. No name or ID number is asked for, everything is worked out in your browser and no data is sent or stored. The PDF report is also generated in your browser.
Source
Chilean national intrauterine growth curves (Alarcón-Pittaluga) up to 40 weeks of corrected age; after that, WHO growth standards using the corrected age.
A support tool for health professionals. It does not replace clinical assessment or the technical standard in force.