whoFetalStandards makes the WHO Fetal Standards available to R users. It has few functions, which can be used to convert fetal biometry to centiles or z-scores. The API is very similar to the gigs package for R, which implements similar standards from the WHO and the INTERGROWTH-21st projects. You can find that package at lshtm-gigs/gigs.
You can install the development version of whoFetalStandards like so:
pak::pkg_install("simpar1471/whoFetalStandards")The WHO published six Fetal standards. All of them are sex-agnostic except for estimated fetal weight, which is different for males and females.
| Acronym | Description | Unit |
|---|---|---|
acfga |
abdominal circumference-for-GA | m |
bpdfga |
biparietal diameter-for-GA | mm |
efwfga |
estimated fetal weight-for-GA | g |
flfga |
femur length-for-GA | mm |
hcfga |
head circumference-for-GA | mm |
flfga |
femur length-for-GA | mm |
Convert fetal biometry to centiles/z-scores with value2zscore() and
value2centile(). These should be used for measurements taken from 98
to 280 days (14 to 40 weeks).
library(whoFetalStandards)
# Convert biparietal diameter values to centiles
value2centile(81, gest_days = 30 * 7, acronym = "bpdfga")
#> [1] 0.9000039
# Convert biparietal diameter values to centiles
value2zscore(81, gest_days = 30 * 7, acronym = "bpdfga")
#> [1] 1.281574The package also includes a simple function for estimating fetal weight in g, using Hadlock’s three-parameter equation.
hadlock_efw(headcirc_cm = 12,
abdocirc_cm = 9.5,
femurlen_cm = 10)
#> [1] 1382.929