Implicaciones para la Clasificación del Crecimiento de Recién Nacidos y Niños Utilizando INTERGROWTH-21st y los...

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.

A secondary data analysis of an observational cohort study.

Five health facilities participating in the Low Birthweight Infant Feeding Exploration (LIFE) study in Malawi and Tanzania.

608 moderately low birthweight (1.5 to < 2.5 kg) infants.

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.

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.

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.

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.