gigs: Fetal, neonatal and infant growth assessment in Stata

About

Produced as part of the Guidance for International Growth Standards (GIGS) project, gigs provides a single, simple interface for working with the WHO Child Growth Standards and outputs from the INTERGROWTH-21^st project. You will find functions for converting between anthropometric measures (e.g. weight or length) to z-scores and centiles, and the inverse. Also included is a command for classifying newborn and infant growth according to published z-score/centile cut-offs.

Installation

The gigs package is available for Stata version 16 and over. You can install the development version of gigs from GitHub using the github module for Stata:

. github install lshtm-gigs/gigs-stata

Alternatively, you can download a stable release of your choice from GitHub using the net install command from Stata. Simply go to the stable release of gigs that you want to download from the releases page on GitHub, and download the zipped archive. Unzip this downloaded archive. Within this unzipped folder will be another folder, inside which will be the .ado/.dta files needed for gigs to work. Put the path to the folder containing the .ado/.dta files in the from() option of net install, and Stata will install the necessary files.

. net install gigs, from("directory/of/unzipped/folder/with/ado/files")

Available standards

• ig_nbs - INTERGROWTH-21^st standards for newborn size

  Component standards

  Acronym	Description	Unit	gest_days() range
  wfga	Weight-or-gestational age	kg	168 to 300 days
  lfga	Length-for-gestational age	cm	168 to 300 days
  hcfga	Head circumference-for-gestational age	cm	168 to 300 days
  wlrfga	Weight-to-length ratio-for-gestational age	kg/cm	168 to 300 days
  ffmfga	Fat-free mass-for-gestational age	kg	266 to 294 days
  bfpfga	Body fat percentage-for-gestational age	%	266 to 294 days
  fmfga	Fat mass-for-gestational age	kg	266 to 294 days

• ig_png - INTERGROWTH-21^st standards for postnatal growth in preterm infants

  Component standards

  Acronym	Description	Unit	xvar() range
  wfa	weight-for-age	kg	27 to ≤64 weeks PMA
  lfa	length-for-age	cm	27 to ≤64 weeks PMA
  hcfa	head circumference-for-age	cm	27 to ≤64 weeks PMA
  wfl	weight-for-length	kg	35 to 65 cm

• ig_fet - INTERGROWTH-21^st fetal standards

  Component standards

  Acronym	Description	Unit	x range
  hcfga	head circumference-for-GA	mm	98 to 280 days
  bpdfga	biparietal diameter-for-GA	mm	98 to 280 days
  acfga	abdominal circumference-for-GA	mm	98 to 280 days
  flfga	femur length-for-GA	mm	98 to 280 days
  ofdfga	occipito-frontal diameter for-GA	mm	98 to 280 days
  efwfga	estimated fetal weight-for-GA	grams	154 to 280 days
  sfhfga	symphisis-fundal height-for-GA	mm	112 to 294 days
  crlfga	crown-rump length-for-GA	mm	58 to 105 days
  gafcrl	GA-for-crown-rump length	days	15 to 95 mm
  gwgfga	gestational weight gain-for-GA	kg	98 to 280 days
  pifga	pulsatility index-for-GA		168 to 280 days
  rifga	resistance index-for-GA		168 to 280 days
  sdrfga	systolic/diastolic ratio-for-GA		168 to 280 days
  tcdfga	transcerebellar diameter-for-GA	mm	98 to 280 days
  gaftcd	GA-for-transcerebellar diameter	days	12-55 mm
  poffga	parietal-occipital fissure-for-GA	mm	105 to 252 days
  sffga	Sylvian fissue-for-GA	mm	105 to 252 days
  avfga	anterior horn of the lateral ventricle-for-GA	mm	105 to 252 days
  pvfga	atrium of the posterior horn of the lateral ventricle-for-GA	mm	105 to 252 days
  cmfga	cisterna magna-for-GA	mm	105 to 252 days
  hefwfga	Hadlock estimated fetal weight-for-GA	g	126 to 287 days

• who_gs - WHO Child Growth Standards for term infants

  Component standards

  Acronym	Description	Unit	xvar() range
  wfa	weight-for-age	kg	0 to 1856 days
  bfa	BMI-for-age	kg/m2	0 to 1856 days
  lhfa	length/height-for-age	cm	0 to 1856 days
  hcfa	head circumference-for-age	cm	0 to 1856 days
  wfl	weight-for-length	kg	45 to 110 cm
  wfh	weight-for-height	kg	65 to 120 cm
  acfa	arm circumference-for-age	cm	91 to 1856 days
  ssfa	subscapular skinfold-for-age	mm	91 to 1856 days
  tsfa	triceps skinfold-for-age	mm	91 to 1856 days

Conversion functions

Each conversion function has similar syntax. The main function call determines the set of standards in use, the acronym parameter specifies which component standard is being used, and the conversion parameter specifies the type of conversion you wish to perform. This conversion parameter can take one of four values: "v2z" (value-to-z-score), "v2c" (value-to-centile), "z2v" (z-score-to-value), "c2v" (centile-to-value). The sex() and sexcode() options supply the non-fetal functions with sex data - without this, these sex-specific growth standards cannot be applied.

INTERGROWTH-21^st Newborn Size standards, including very preterm

This function can be used to convert between measurements and z-scores/centiles in each of the INTERGROWTH-21^st Newborn Size Standards.

The extend option, when specified, allows the function to use extrapolated versions of these INTERGROWTH-21^st standards which can take gestational ages from 154 to 314 days (22⁺⁰ to ⁴⁴⁺⁶ weeks) when acronym is one of "wfga", "lfga", or "hcfga". Our process for extrapolating these standards is documented here.

INTERGROWTH-21^st Postnatal Growth standards

This function can be used to convert between measurements and z-scores/centiles in each of the INTERGROWTH-21^st Postnatal Growth of Preterm Infants Standards.

INTERGROWTH-21^st Fetal Growth standards

This function can be used to convert between measurements and z-scores/centiles in each of the INTERGROWTH-21^st Fetal standards.

WHO Child Growth Standards

This function can be used to convert between measurements and z-scores/centiles in each of the WHO Child Growth Standards.

Classification command

The gigs_classify_growth command is used to classify infant growth according to published cut-offs. These publications are discussed in the attached paper.

The outcome argument is used to pick specific growth analyses, or you can run all growth analyses by using all.

Available growth outcomes

• all - Generate variables for all growth outcomes

• sfga - Generate variables for size for gestational age

  Values and labels for generated variables sfga and sfga_severe

  Value	Meaning	Centile range
  -2	Severely small for gestational age	<3rd
  -1	Small for gestational age (SGA)	<10th
  0	Appropriate for gestational age (AGA)	10th to 90th
  1	Large for gestational age (LGA)	>90th

• svn - Generate variables for small vulnerable newborns

  Values and labels for generated variable svn

  Value	Meaning	Term Status	Centile range
  -4	Preterm SGA	Preterm	<10th
  -3	Preterm AGA	Preterm	10th to 90th
  -2	Preterm LGA	Preterm	>90th
  -1	Term SGA	Term	<10th
  0	Term AGA	Term	10th to 90th
  1	Term LGA	Term	>90th

• stunting - Generate variables for stunting

  Values and labels for generated variables stunting and stunting_outliers

  Value	Meaning	Z-score range
  -2	Severe stunting	-5 to -3
  -1	Stunting	-3 to -2
  0	Not stunting	-2 to 5
  -10	Implausible	<-5 or >5

• wasting - Generate variables for wasting

  Values and labels for generated variables wasting and wasting_outliers

  Value	Meaning	Z-score range
  -2	Severe wasting	-5 to -3
  -1	Wasting	-3 to -2
  0	Not wasting	-2 to 2
  1	Overweight	2 to 5
  -10	Implausible	<-5 or >5

• wfa - Generate variables for weight-for-age

  Values and labels for generated variables wfa and wfa_outliers

  Value	Meaning	Z-score range
  -2	Severely underweight	-6 to -3
  -1	Underweight	-3 to -2
  0	Normal weight	-2 to 2
  1	Overweight	2 to 5
  -10	Implausible	<-6 or >5

• headsize - Generate variables for head size

  Values and labels for generated variable headsize

  Value	Meaning	Z-score range
  -2	Severe microcephaly	<-3
  -1	Microcephaly	-3 to -2
  0	Normal weight	-2 to 2
  1	Microcephaly	-3 to -2
  2	Severe microcephaly	>3

Examples

This section illustrates a possible use case using life6mo.dta, an extract of data from the Low birthweight Infant Feeding Exploration (LIFE) Study. It contains weight measurements for term and preterm infants from birth (visitweek == 0) to around six months of age (visitweek == 26).

. use life6mo, clear
. keep id gestage sex visitweek pma age_days weight_g
. local 37weeks 7 * 37
. list in f/9, noobs abbreviate(10) sep(9)
 __________________________________________________________
|  id  gestage  sex visitweek   pma   age_days   weight_g  |
|   1      273    1         0   273          0   2300      |
|   1      273    1         1   280          7   2185      |
|   1      273    1         2   288         15   2325      |
|   1      273    1         4   301         28   2575      |
|   1      273    1         6   316         43   3410      |
|   1      273    1         10  344         71   4262.3333 |
|   1      273    1         14  376        103   5050      |
|   1      273    1         18  399        126   5431.6667 |
|   1      273    1         26  460        187   5835      |
 ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾

Conversion

We can use the conversion functions listed above to generate weight-for-age z-scores (WAZs) in the different study populations (i.e. term vs preterm) and measurement timings (i.e. z-scores for newborns with INTERGROWTH-21^st Newborn Size Standards, WHO/INTERGROWTH Postnatal standards after birth).

. egen double waz_nbs = ig_nbs(weight_g/1000, "wfga", "v2z") ///
>     if age_days == 0, ///
>     gest_days(gestage) sex(sex) sexcode(m=1, f=2)
(2,432 missing values generated)

. egen double waz_who = who_gs(weight_g/1000, "wfa", "v2z") ///
>     if age_days > 0 & gestage >= `37weeks´, ///
>     xvar(age_days) sex(sex) sexcode(m=1, f=2)
(1,360 missing values generated)

. gen pma_weeks = pma / 7
. egen double waz_png = ig_png(weight_g/1000, "wfa", "v2z") ///
>     if age_days > 0 & gestage < `37weeks´, ///
>     xvar(pma_weeks) sex(sex) sexcode(m=1, f=2)
(1,463 missing values generated)
. drop pma_weeks

We can then combine these WAZs into one overall waz variable:

. gen double waz = waz_who if gestage > `37weeks´
(1,508 missing values generated)
. replace waz = waz_png if gestage < `37weeks´
(1,026 real changes made)
. replace waz = waz_nbs if age_days == 0
(57 real changes made)

. list visitweek gestage pma waz_* waz in f/9, noobs sep(9)
 ____________________________________________________________________
| visitw~k  gestage  pma    waz_nbs      waz_who  waz_png        waz |
|        0      273  273  -2.298544            .        .  -2.298544 |
|        1      273  280          .    -3.028356        .  -3.028356 |
|        2      273  288          .   -3.2685948        . -3.2685948 |
|        4      273  301          .   -3.6824586        . -3.6824586 |
|        6      273  316          .   -2.7962372        . -2.7962372 |
|       10      273  344          .   -2.5495876        . -2.5495876 |
|       14      273  376          .   -2.3102437        . -2.3102437 |
|       18      273  399          .   -2.3030732        . -2.3030732 |
|       26      273  460          .   -2.8157742        . -2.8157742 |
 ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾

This waz variable can then be used to determine whether infants are underweight at different age points, or to track the growth trajectory of individual children.

Classification

This dataset contains information on weight at birth, so could be used to calculate size-for-gestational age classifications. The gigs_classify_growth command will automatically pick out birth observations, and compute size-for-GA in these observations:

. use life6mo, clear
. gen wt_kg = weight_g / 1000
. gigs_classify_growth sfga, ///
>     gest_days(gestage) sex(sex) sexcode(m=1, f=2) ///
>     weight_kg(wt_kg) id(id)
Requested outcomes:
    Size-for-gestational age (sfga)
NOTE: There were 231 birth observations where `age_days' > 0.5.
NOTE: There was 1 birth measure where an infant was too old for the 
      INTERGROWTH-21st Newborn Size standards (`gest_age' > 300).
      This infant will be assessed with the WHO Growth Standards instead.
Supplied data:
    Weight in kg
Running analyses. New/replaced variables:
    Generated new variable birthweight_centile.
    Generated new variable sfga.
    Generated new variable sfga_severe.

. tab sfga

       sfga |      Freq.     Percent        Cum.
------------+-----------------------------------
        SGA |        185       64.46       64.46
        AGA |         88       30.66       95.12
        LGA |         14        4.88      100.00
------------+-----------------------------------
      Total |        287      100.00

Known issues and bug reporting

We request that users note any bugs, issues, or feature requests on the GitHub issues page.

Solving gigs_ipolate_coeffs() not found

Some users have reported issues running the who_gs() and ig_nbs() functions, due to issues with Stata version compatability and gigs_ipolate_coeffs.mo. This can happen when the .mo file is either too recent for your version of Stata. Run the following command to see if the file is present, and if Stata can use it:

. mata: mata which gigs_ipolate_coeffs

Assuming you get a result which indicates version incompatability, you can take these steps to resolve the issue.

1. Download gigs_ipolate_coeffs.mata to your computer, to either your working directory or somewhere you specify.
2. In the downloaded version of gigs_ipolate_coeffs.mata:
   1. Edit line 83 (mata mosave gigs_ipolate_coeffs(), replace) by adding the dir() option, so you save gigs_ipolate_coeffs.mo somewhere specific. It should look something like this: mata mosave gigs_ipolate_coeffs(), replace dir("path/to/a/directory").
   2. Remove line 2 (version 16) from the downloaded file.
3. Open and run your edited version of gigs_ipolate_coeffs.mata in your Stata. Stata should inform you that file gigs_ipolate_coeffs.mo created, or something similar.
4. By default, the files for gigs are located in your Stata PLUS directory. Use sysdir to find the location of your PLUS directory. On Windows, the output will look something like this:

. sysdir
   STATA:  C:\Program Files\Stata18\
    BASE:  C:\Program Files\Stata18\ado\base\
    SITE:  C:\Program Files\Stata18\ado\site\
    PLUS:  C:\Users\your_user\ado\plus\
PERSONAL:  C:\Users\your_user\ado\personal\
OLDPLACE:  c:\ado\

5. Go to the PLUS directory and look at the g subdirectory. This should contain a copy of gigs_ipolate_coeffs.mo, but it is incompatible with your Stata version. Replace it with the version of gigs_ipolate_coeffs.mo you created in step 3, and restart Stata. The errors you've been getting should now stop appearing.

If you reinstall gigs at any point, for example to retrieve package updates, you'll need to repeat these compilation + file replacement steps again. If these instructions don't work or you need more specific guidance, let us know on the GitHub issues page.

Authors

S. R. Parker
Maternal, Adolescent, Reproductive, and Child Health Centre
London School of Hygiene & Tropical Medicine

Dr L. Vesel
Ariadne Labs, Brigham and Women’s Hospital
Harvard T.H. Chan School of Public Health

Professor E. O. Ohuma
Maternal, Adolescent, Reproductive, and Child Health Centre
London School of Hygiene & Tropical Medicine

References

• INTERGROWTH-21^st Newborn Size standards (including very preterm)
  • Villar J, Cheikh Ismail L, Victora CG, Ohuma EO, Bertino E, Altman DG, 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):857-68. doi: 10.1016/S0140-6736(14)60932-6
  • Villar J, Giuliani F, Fenton TR, Ohuma EO, Ismail LC, Kennedy SH et al. INTERGROWTH-21st very preterm size at birth reference charts. Lancet 2016, 387(10021):844-45. doi: 10.1016/S0140-6736(16)00384-6
  • Villar J, Puglia FA, Fenton TR, Ismal LC, Staines-Urias E, Giuliani F, et al. Body composition at birth and its relationship with neonatal anthropometric ratios: the newborn body composition study of the INTERGROWTH-21st project. Pediatric Research 2017, 82:305-316. doi: 10.1038/pr.2017.52
• INTERGROWTH-21^st Postnatal Growth of Preterm Infants standards
  • Villar J, Giuliani F, Bhutta ZA, Bertino E, Ohuma EO, Ismail LC et al. Postnatal growth standards for preterm infants: the Preterm Postnatal Follow-up Study of the INTERGROWTH-21st Project. Lancet Glob Health 2015, 3(11):e681-e691. doi: 10.1016/S2214-109X(15)00163-1
• INTERGROWTH-21^st Fetal standards
  • Papageorghiou AT, Ohuma EO, Altman DG, Todros T, Cheikh Ismail L, Lambert A et al. International standards for fetal growth based on serial ultrasound measurements: the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project. Lancet 2014, 384(9946):869-79. doi: 10.1016/S0140-6736(14)61490-2
  • Stirnemann J, Villar J, Salomon LJ, Ohuma EO, Lamber A, Victoria CG et al. International Estimated Fetal Weight Standards of the INTERGROWTH-21st Project. Ultrasound Obstet Gynecol 2016, 49:478-486 doi: 10.1002/uog.17347
  • Stirnemann J, Salomon LJ, Papageorghiou AT. INTERGROWTH-21st standards for Hadlock’s estimation of fetal weight. Ultrasound Obstet Gynecol 2020, 56(6):946-948 doi: 10.1002/uog.22000
  • Papageorghiou AT, Ohuma EO, Gravett MG, Lamber A, Noble JA, Pang R et al. International standards for symphysis-fundal height based on serial measurements from the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project: prospective cohort study in eight countries. BMJ 2016, 355:i5662 doi: 10.1136/bmj.i5662
  • Papageorghiou AT, Kennedy SH, Salomon LJ, Ohuma EO, Cheikh Ismail L, Barros FC et al. International standards for early fetal size and pregnancy dating based on ultrasound measurement of crown-rump length in the first trimester of pregnancy. Ultrasound Obstet Gynecol 2014, 44(6):641-48 doi: 10.1002/uog.13448
  • Cheikh Ismail L, Bishop DC, Pang R, Ohuma EO, Kac G, Abrams B et al. Gestational weight gain standards based on women enrolled in the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project: a prospective longitudinal cohort study. BMJ 2016, 352:i555 doi: 10.1136/bmj.i555
  • Drukker L, Staines-Urias E, Villar J, Barros FC, Carvalho M, Munim S et al. International gestational age-specific centiles for umbilical artery Doppler indices: a longitudinal prospective cohort study of the INTERGROWTH-21st Project. Am J Obstet Gynecol 2021, 222(6):602.e1-602.e15 doi: 10.1016/j.ajog.2020.01.012
  • Rodriguez-Sibaja MJ, Villar J, Ohuma EO, Napolitano R, Heyl S, Carvalho M et al. Fetal cerebellar growth and Sylvian fissure maturation: international standards from Fetal Growth Longitudinal Study of INTERGROWTH-21st Project Ultrasound Obstet Gynecol 2021, 57(4):614-623 doi: 10.1002/uog.22017
  • Napolitano R, Molloholli M, Donadono V, Ohuma EO, Wanyonyi SZ, Kemp B et al. International standards for fetal brain structures based on serial ultrasound measurements from Fetal Growth Longitudinal Study of INTERGROWTH-21st Project Ultrasound Obstet Gynecol 2020, 56(3):359-370 doi: 10.1002/uog.21990
• WHO Child Growth Standards
  • de Onis M, Garza C, Victora CG, Onyango AW, Frongillo EA, Martines J. The WHO Multicentre Growth Reference Study: planning, study design, and methodology Food Nutr Bull. 2004, 25(1 Suppl):S15-26. doi: 10.1177/15648265040251s104
  • World Health Organisation. WHO child growth standards: length/height-for-age, weight-for-age, weight-for-length, weight-for-height and body mass index-for-age: methods and development. Technical report, WHO, Geneva, 2006.
  • World Health Organisation. WHO child growth standards: head circumference-for-age, arm circumference-for-age, triceps skinfold-for-age and subscapular skinfold-for-age: methods and development. Technical report, WHO, Geneva, 2007.