INTERGROWTH-21st Calculator
Assess newborn size and fetal growth standards using INTERGROWTH-21st project guidelines. Calculate centiles and Z-scores for weight, length, and head circumference.
About
In the field of neonatology and pediatrics, precision is not a luxury; it is a necessity. The INTERGROWTH-21st Calculator is a specialized clinical tool designed to assess newborn size and monitor fetal growth patterns against the global standards established by the INTERGROWTH-21st Consortium. Unlike older reference charts that were often based on local populations or descriptive studies, these standards prescribe how fetuses and newborns should grow under optimal health conditions, making this tool applicable across diverse ethnic and geographical populations.
Accurate growth monitoring is the cornerstone of early detection for conditions such as Intrauterine Growth Restriction (IUGR) or macrosomia. By inputting gestational age, gender, and anthropometric measurements (weight, length, head circumference), clinicians can instantly derive exact percentiles and Z-scores. This data is critical for determining nutritional needs, planning interventions, and predicting long-term neurodevelopmental outcomes.
Formulas
The calculator utilizes the LMS method (Lambda-Mu-Sigma) to normalize the distribution of anthropometric data. This allows for the calculation of Z-scores, which represent how many standard deviations a measurement is from the mean.
Where X is the physical measurement, M is the median, S is the coefficient of variation, and L is the Box-Cox power to remove skewness. If L is close to zero, the natural logarithm is used instead.
Reference Data
| Gestational Age (Weeks) | Parameter | 3rd Centile | 50th Centile (Median) | 97th Centile |
|---|---|---|---|---|
| 24 Weeks | Weight (kg) | 0.51 | 0.66 | 0.86 |
| 28 Weeks | Weight (kg) | 0.89 | 1.15 | 1.49 |
| 32 Weeks | Weight (kg) | 1.45 | 1.88 | 2.43 |
| 36 Weeks | Weight (kg) | 2.16 | 2.78 | 3.56 |
| 40 Weeks | Weight (kg) | 2.78 | 3.62 | 4.63 |
| 24 Weeks | Head Circ. (cm) | 20.8 | 22.9 | 25.0 |
| 32 Weeks | Head Circ. (cm) | 27.5 | 29.8 | 32.1 |
| 40 Weeks | Head Circ. (cm) | 32.1 | 34.7 | 37.3 |
| 24 Weeks | Length (cm) | 29.8 | 32.4 | 35.0 |
| 40 Weeks | Length (cm) | 46.2 | 50.3 | 54.4 |