Produced as part of the Guidance for International Growth Standards project, gigs provides a single, simple interface for working with the WHO Child Growth standards and outputs from the INTERGROWTH-21st project. You will find functions for converting from anthropometric measures (e.g. weight or length) to z-scores and centiles, and the inverse. Also included are functions for classifying newborn and infant growth according to literature-based cut-offs.
# You can install the development version from GitHub with `remotes`:
# install.packages("remotes")
remotes::install_github(repo = "lshtm-gigs/gigs")-
ig_nbs- INTERGROWTH-21st Newborn Size standards (including very preterm)Component standards
Acronym Description Unit gest_daysrangewfgaWeight-or-gestational age kg 168 to 300 days lfgaLength-for-gestational age cm 168 to 300 days hcfgaHead circumference-for-gestational age cm 168 to 300 days wlrfgaWeight-to-length ratio-for-gestational age kg/cm 168 to 300 days ffmfgaFat-free mass-for-gestational age kg 266 to 294 days bfpfgaBody fat percentage-for-gestational age % 266 to 294 days fmfgaFat mass-for-gestational age kg 266 to 294 days -
ig_png- INTERGROWTH-21st Postnatal Growth of Preterm Infants standardsComponent standards
Acronym Description Unit xrangewfaweight-for-age kg 27 to <64 exact weeks lfalength-for-age cm 27 to <64 exact weeks hcfahead circumference-for-age cm 27 to <64 exact weeks wflweight-for-length kg 35 to 65 cm -
who_gs- WHO Child Growth Standards for term infantsComponent standards
Acronym Description Unit xrangewfaweight-for-age kg 0 to 1856 days bfaBMI-for-age kg/m2 0 to 1856 days lhfalength/height-for-age cm 0 to 1856 days hcfahead circumference-for-age cm 0 to 1856 days wflweight-for-height kg 45 to 110 cm wfhweight-for-length kg 65 to 120 cm acfaarm circumference-for-age cm 91 to 1856 days ssfasubscapular skinfold-for-age mm 91 to 1856 days tsfatriceps skinfold-for-age mm 91 to 1856 days
Conversion functions are named according to the set of standards in use,
the component standard from that set, then the type of conversion. For
example, to convert values to z-scores in the weight-for-GA standard
from the INTERGROWTH-21st Newborn Size Standards would be:
ig_nbs/_wfga/_value2zscore()
Similarly, the conversion of length-for-age values to centiles in term and preterm infants could be performed with the WHO Child Growth standards and INTERGROWTH-21st Postnatal Growth of Preterm Infants standards, respectively:
- Term infants:
who_gs/_lhfa/_value2zscore() - Preterm infants:
ig_png/_lfa/_value2centile()
If the component standard is not included in the function call, it
should be passed to the acronym parameter of the general function
call. For example, these two function calls would behave in the same
way:
ig_nbs_value2zscore(y = 25.7, gest_days = 182, sex = "F", acronym = "hcfga") |>
round(digits = 2)
#> [1] 1.18
ig_nbs_hcfga_value2zscore(headcirc_cm = 25.7, gest_days = 182, sex = "F") |>
round(digits = 2)
#> [1] 1.18A vector of acronym values can be used if you want to convert with
different standards for each input.
These functions allow easy conversion from measured values to z-scores or centiles for the standard used.
# Convert from z-scores for individual values...
ig_nbs_value2zscore(y = 0.785, gest_days = 182, sex = "F", acronym = "wfga") |>
round(digits = 2)
#> [1] 0
# .. or for multiple inputs
ig_nbs_wfga_value2centile(weight_kg = 0.785,
gest_days = seq(175, 196, by = 7),
sex = "F") |>
round(digits = 2)
#> [1] 0.75 0.50 0.25 0.09
# You can do the same for centiles
ig_png_wfa_value2centile(weight_kg = c(2.86, 3.12, 3.12, 3.43, 3.77, 4.10),
pma_weeks = 40,
sex = "M") |>
round(digits = 2)
#> [1] 0.10 0.25 0.25 0.50 0.75 0.90These functions convert z-scores to expected anthropometric measurements. They are mostly useful for the creation of reference curves (see below).
# Convert from z-scores for individual values...
ig_nbs_zscore2value(z = 0, gest_days = 182, sex = "F", acronym = "wfga") |>
round(digits = 3)
#> [1] 0.785
# .. or for multiple inputs
ig_nbs_wfga_zscore2value(z = 0, gest_days = seq(182, 204, by = 7), sex = "F") |>
round(digits = 3)
#> [1] 0.785 0.893 1.013 1.147
# You can do the same for centiles
ig_png_wfa_centile2value(p = c(0.1, 0.25, 0.5, 0.75, 0.9),
pma_weeks = 40,
sex = "M") |>
round(digits = 2)
#> [1] 2.87 3.12 3.43 3.77 4.11We can use gigs to generate reference curves for the standards by
getting curves for the expected weight at multiple z-scores across
multiple gestational ages. We would usually recommend
ggplot2 for such visualisation, but
do not use it here to reduce our package’s dependencies.
z_score_range <- -2:2
gestage_range <- 168:230
ref <- mapply(z_score_range,
FUN = function(z) {
gigs::ig_nbs_wfga_zscore2value(z = z,
gest_days = gestage_range,
sex = "F")
})
matplot(ref, x = gestage_range, col = 1:5, type = "l", lty = 2:6,
xlab = "Gestational age (days)",
ylab = "Weight (kg)")
title(main = "Weight-for-GA in very preterm newborns")
legend(x = min(gestage_range) + 1, y = ref[length(ref)], legend = 2:-2,
title = "Z-score", col = 5:1, lty = 2:6)These functions allow for quick identification of at-risk infants through classification of suboptimal growth. The cut-offs used are sourced from research literature; you can check the function documentation to see these sources.
# Size for gestational age
classify_sga(
weight_kg = c(2.1, 3.2, 4.5),
gest_days = c(252, 259, 290),
sex = "M"
)
#> [1] SGA AGA LGA
#> Levels: SGA AGA LGA
# Small vulnerable newborns
classify_svn(
weight_kg = c(2.1, 3.2, 4.5),
gest_days = c(252, 259, 290),
sex = "M"
)
#> [1] Preterm SGA Term AGA Term LGA
#> Levels: Preterm SGA Preterm AGA Preterm LGA Term SGA Term AGA Term LGA
# Stunting, i.e. low length increase relative to age
classify_stunting(
lenht_cm = c(42.3, 75.4, 72.83),
age_days = c(252, 525, 245),
gest_days = c(238, 259, 266),
sex = "M"
)
#> [1] stunting_severe stunting normal
#> Levels: stunting_severe stunting normal
# Wasting, i.e. low weight increase relative to length/height
classify_wasting(
weight_kg = c(5.75, 2.18, 5.30, 6.75),
lenht_cm = c(67.7, 46.6, 55.8, 80.1),
gest_days = c(268, 247, 250, 278),
age_days = c(45, 33, 230, 278),
sex = c("F", "M", "F", "M"),
)
#> [1] wasting_severe wasting normal wasting_severe
#> Levels: wasting_severe wasting normal overweight
# Weight-for-age, i.e. low weight increase relative to age
classify_wfa(
weight_kg = c(2.1, 7.2, 6.1, 9.1, 9.4),
age_days = c(435, 501, 323, 201, 154),
gest_days = c(36, 27, 37, 40, 28),
sex = c("M", "M", "F", "F", "F")
)
#> [1] underweight_severe underweight_severe <NA> <NA>
#> [5] overweight
#> Levels: underweight_severe underweight normal overweight