This version was machine-translated from German and has not been medically reviewed. The authoritative version is the German version.

INTERGROWTH-21st size at birth (33+0 to 42+6 weeks)

Birth weight, length and head circumference according to the INTERGROWTH-21st standard, with z-score and SGA/LGA

About this calculator

Percentiles and z-scores of birth weight, length and head circumference according to the INTERGROWTH-21st Newborn Size Standard (Villar 2014), to the exact day from 33+0 to 42+6 weeks. Calculation uses the model behind the official tables (skew-t distribution, GAMLSS), not approximations. Below 33+0 weeks the calculator applies to very preterm infants.

Postmenstrual age = gestational age at birth + age since birth. For classification at birth (SGA/AGA/LGA), completed weeks are customary; here the curves are interpolated to the day.

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Reference and license

INTERGROWTH-21st newborns – 33+0 to 42+6 weeks (gestational age at birth).
Villar J, Cheikh Ismail L, Victora CG, Ohuma EO, et al. International standards for newborn weight, length, and head circumference by gestational age and sex: the Newborn Cross-Sectional Study of the INTERGROWTH-21st Project. Lancet. 2014;384(9946):857–868. License: terms of use of the INTERGROWTH-21st data not clarified (portal intergrowth21.com public and free of charge; whether use in a calculator is permitted is not documented). Coefficients from the R package gigs (LSHTM, github.com/lshtm-gigs/gigs); its GPL ≥ 3 license applies to the R code, not to the data. Only the calculation has been reproduced here, no code adopted. The model parameters (mu, sigma, nu, tau) are not given in the publication; according to gigs, Eric Ohuma (INTERGROWTH-21st) supplied them. Source
Standard from healthy pregnancies in 8 countries. Applies only to birth measurements. The model is a skew-t distribution (skew-t type 3, GAMLSS), not an LMS curve. Checked against the published tables: at most one rounding place of deviation (0.01 kg or 0.1 cm).

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Note

Calculation aid for healthcare professionals. Percentiles and z-scores describe the position of a measured value in the reference population; clinical assessment remains with the treating physician.

Review date of the German original: 2026-11-08 · Methodology

Frequently asked questions

Why a separate calculator for 24 to 32 weeks?

For children under 33 weeks, INTERGROWTH-21st has its own, simpler model (Villar 2016, normal distribution). It is a reference of observed births, not a standard. Between 32+6 and 33+0 weeks the percentiles therefore jump somewhat.

How closely do the values match the official tables?

The tables were recalculated for all days from 33+0 to 42+6 weeks. Compared with the z-score tables, no value deviates by more than one digit after rounding (0.01 kg and 0.1 cm respectively). The percentile tables deviate somewhat more in a few places: for girls' weight from 33+0 to about 33+6 weeks by up to 0.015 kg (for example 33+0, P50: table 1.86 kg, calculator 1.85 kg). The reason lies in the sources themselves: the z-score and percentile tables give different median values there (1.85 and 1.86 kg).