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Implications for Newborn and Child Growth Classification Using INTERGROWTH-21st and WHO Child Growth Standards
Linda Vesel1, Sara Strout2, Simon Parker2
1Ariadne Labs, Harvard T.H. Chan School of Public Health/Brigham and Women's Hospital, Boston, Massachusetts, USA.
Insights
The INTERGROWTH-21st (IG-21st) standards offer more accurate growth assessments for preterm infants compared to WHO Child Growth Standards (WHO GS). Using IG-21st standards improves classification and monitoring, especially in the first year of life.
Area of Science:
- Pediatrics
- Neonatology
- Growth Monitoring
Background:
- Accurate growth assessment is crucial for identifying deviations from expected patterns in infants.
- Existing growth standards may not adequately represent diverse infant populations, particularly preterm infants.
- The WHO Child Growth Standards (WHO GS) and INTERGROWTH-21st Standards (IG-21st) are widely used but may yield different classifications.
Purpose of the Study:
- To compare the classification and interpretation of infant growth trajectories using the WHO GS and IG-21st standards.
- To evaluate the impact of different growth standards on identifying growth abnormalities in low birthweight infants.
Main Methods:
- Secondary data analysis of an observational cohort study involving 608 moderately low birthweight infants in Malawi and Tanzania.
- Calculation of Z-scores (weight-for-age, length-for-age, head circumference-for-age) at birth and longitudinally up to 24 months using both WHO GS and IG-21st standards.
- Construction of conditional growth models to assess deviations from mean growth patterns within gestational age subgroups.
Main Results:
- At birth, IG-21st Newborn Size Standard (NBS) z-scores were higher than WHO GS, particularly in lower gestational age subgroups.
- The proportion of preterm infants classified with Z-scores below -2 was significantly lower using IG-21st Preterm Postnatal Standards (PPS) compared to WHO GS (e.g., weight: 6.1% vs. 95.6%).
- Between-standard z-score differences were largest in preterm infants from birth to 6 months, diminishing by 6-12 months, with minimal differences observed in term infants.
Conclusions:
- The WHO GS alone may misclassify the growth status of preterm and term infants, especially at birth and in early infancy.
- The IG-21st standards provide more appropriate GA-specific classifications, aligning better with expected growth patterns and supporting accurate monitoring.
- Recommendations include using IG-21st NBS at birth, IG-21st PPS from 27 to 64 weeks postmenstrual age, and WHO GS thereafter.
Objective:
The aim of this study was to assess how the use of the WHO Child Growth Standards (WHO GS) and the INTERGROWTH-21st Standards (IG-21st) affect the classification and interpretation of growth trajectories.
Design:
A secondary data analysis of an observational cohort study.
Setting:
Five health facilities participating in the Low Birthweight Infant Feeding Exploration (LIFE) study in Malawi and Tanzania.
Population Or Sample:
608 moderately low birthweight (1.5 to < 2.5 kg) infants.
Methods:
Z-scores for weight-for-age (WAZ), length-for-age (LAZ), and head circumference-for-age (HCAZ) were calculated at birth using both the WHO GS and the IG-21st Newborn Size Standard (IG-21st NBS). Longitudinal trajectories were assessed over three periods (birth-6 months, 6-12 months and 12-24 months) using WHO GS and IG-21st Preterm Postnatal Standards (IG-21st PPS). Between 12 and 24 months, all infants were assessed using WHO GS. Conditional growth models were constructed to evaluate deviation from mean growth patterns within GA subgroups.
Main Outcome Measures:
WAZ, LAZ and HCAZ z-scores; prevalence of z-scores < -2, and absolute and conditional growth trajectory differences between WHO and IG-21st standards across three postnatal intervals.
Results:
At birth, IG-21st NBS z-scores were higher than WHO GS values especially in lower GA subgroups, particularly for LAZ and HCAZ. The proportion of infants with < -2 z-scores was substantially lower with IG-21st PPS than WHO GS in preterm infants for weight (6.1% vs. 95.6%), length (14.4% vs. 89.2%) and head circumference (4.2% vs. 53.5%), respectively. From birth to 6 months, between-standard z-score differences (IG-21st PPS minus WHO GS) were largest in preterm infants (preterm overall: WAZ: +1.78, LAZ: +1.64, HCAZ: +1.80). From 6 to 12 months, differences persisted but were smaller (preterm overall: WAZ: +0.57, LAZ: +0.79, HCAZ: +0.54), while term infants showed minimal differences between the two standards.
Conclusions:
The application of the WHO GS alone may misclassify preterm and term infants' growth status, particularly at birth and during early infancy. The use of the IG-21st standards provides GA-specific classifications that may more closely align with expected growth patterns in term and preterm infants and could support more accurate monitoring during the first year of life. Based on these implications analyses, we recommend the use of the IG-21st NBS for cross-sectional assessment at birth, the IG-21st PPS from 27 to 64 weeks postmenstrual age, and the WHO GS for all babies thereafter.
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