RT journal article
T1 Temporal External Validation of a Customized Fetal Body Mass Index Percentile Model for Neonatal Nutritional Status Assessment
A1 Fernández Alba, Juan Jesús
A1 Castillo Lara, María
A1 Gutiérrez Palomino, Laura
A1 Castro Peñas, José
A1 Quintero Prado, Rocío
A1 González Macías, Carmen
A2 Materno-Infantil y Radiología
K1 predictive model
K1 decision curve analysis
K1 external validation
K1 diagnostic tools
K1 Ponderal Index
K1 fetal nutritional status
K1 neonatal nutritional status
K1 fetal growth
AB Background/Objectives: Accurate identification of neonatal malnutrition is essential foroptimizing perinatal care and reducing adverse outcomes. Traditional birthweight-basedmethods fail to account for body proportionality, limiting their ability to distinguish constitutionallysmall or large neonates from those with true nutritional abnormalities. Wepreviously developed a customized fetal body mass index (cFBMI) percentile model thatincorporates both weight and length, adjusted for maternal and fetal characteristics. Thisstudy aims to perform a temporal external validation of the cFBMI model following theRiley et al. framework, comparing its performance against the GROW customized birthweightmodel and the INTERGROWTH-21st population-based standard. Methods: Atemporal validation study was conducted using singleton deliveries from Hospital Universitariode Puerto Real, Cádiz, Spain. The development cohort comprised 7864 deliveries(2002–2021); the validation cohort comprised 4441 deliveries (2022–2025). Inclusion criteria:singleton pregnancy, gestational age of 33–42 + 6 weeks, birthweight of 500–6000 g,known neonatal sex and length, and complete maternal data. The Ponderal Index (PI =weight/length3 × 100) stratified by sex and gestational age served as the gold standard(undernutrition: PI < p10; overnutrition: PI > p90). Discrimination was assessed using thearea under the receiver operating characteristic curve (AUC) with bootstrap 95% confidenceintervals (2000 iterations) and DeLong tests. Calibration was evaluated by comparingobserved versus expected proportions across percentile categories. Clinical utility wasassessed using decision curve analysis (DCA). Temporal stability was quantified by comparingAUCs and Brier scores between the development and validation cohorts. Results:In the validation cohort (n = 4441), cFBMI demonstrated superior discrimination for bothundernutrition (AUC: 0.962) and overnutrition (AUC: 0.961) compared with GROW(AUC: 0.751 and 0.676, respectively) and INTERGROWTH-21st (AUC: 0.756 and 0.682,respectively); all DeLong comparisons p < 0.0001. The cFBMI exhibited excellent temporalstability (ΔAUC = −0.004 for undernutrition, +0.002 for overnutrition) and superior calibration(observed proportions: 9.6%/81.7%/8.8% vs. expected 10%/80%/10%; χ2 = 9.22, p =0.010). The decision curve analysis confirmed the superior net benefit of cFBMI across allthreshold probabilities. Conclusions: The customized fetal BMI percentile model demonstratesexcellent and temporally stable discriminative performance in this single-institutiontemporal validation study, with superior calibration and apparent advantages in clinical utility as determined by decision curve analysis compared with existing methods.Its integration of body proportionality provides conceptual alignment with the PonderalIndex gold standard. These findings are promising but require confirmation through externalmulticenter validation before clinical implementation can be recommended. Althoughthe mathematical relationship between the index test (weight/length2) and the referencestandard (weight/length3) should be considered when interpreting the magnitudeof discrimination metrics, validation against independent clinical outcomes is an essentialnext step. The cFBMI thus provides a proportionality-aware nutritional metric whose primarydiscriminative advantage over weight-based methods is realized at and beyond themoment of birth, and which is forward-compatible with emerging modalities for independentprenatal fetal length estimation.
PB MDPI
SN 2075-4418
YR 2026
FD 2026-05-22
LK http://hdl.handle.net/10498/39655
UL http://hdl.handle.net/10498/39655
LA eng
DS Repositorio Institucional de la Universidad de Cádiz
RD 06-nov-2026