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Temporal External Validation of a Customized Fetal Body Mass Index Percentile Model for Neonatal Nutritional Status
Juan Jesús Fernández Alba1,2,3, María Castillo Lara1,2, Laura Gutiérrez Palomino1
1Department of Obstetrics and Gynaecology, University Hospital of Puerto Real, 11510 Cadiz, Spain.
Diagnostics (Basel, Switzerland)
|June 12, 2026
Summary
A new customized fetal body mass index (cFBMI) model accurately identifies neonatal malnutrition, outperforming traditional methods. This proportionality-aware metric shows excellent temporal stability and clinical utility, promising improved perinatal care.
Area of Science:
- Neonatalogy and Perinatal Medicine
- Nutritional Assessment
- Biostatistics and Epidemiology
Background:
- Accurate identification of neonatal malnutrition is critical for optimizing perinatal care and outcomes.
- Traditional birthweight-based methods lack the ability to account for body proportionality, potentially misclassifying neonates.
- A previously developed customized fetal body mass index (cFBMI) model incorporates weight and length, adjusted for maternal and fetal factors.
Purpose of the Study:
- To perform a temporal external validation of the cFBMI percentile model.
- To compare the performance of cFBMI against the GROW customized birthweight model and the INTERGROWTH-21st standard.
- To assess the discriminative ability, calibration, and clinical utility of the cFBMI model.
Main Methods:
- A temporal validation study utilizing singleton deliveries from Hospital Universitario de Puerto Real (development cohort: 2002-2021; validation cohort: 2022-2025).
- Inclusion criteria included gestational age (33-42 + 6 weeks), birthweight (500-6000 g), and complete neonatal and maternal data.
- Discrimination was assessed using AUC with DeLong tests; calibration was evaluated by comparing observed vs. expected proportions; clinical utility was assessed via decision curve analysis (DCA).
Main Results:
- The cFBMI model demonstrated superior discrimination for both undernutrition (AUC: 0.962) and overnutrition (AUC: 0.961) compared to GROW and INTERGROWTH-21st standards (p < 0.0001).
- cFBMI exhibited excellent temporal stability (ΔAUC: -0.004 for undernutrition, +0.002 for overnutrition) and superior calibration.
- Decision curve analysis confirmed the superior net benefit of cFBMI across all threshold probabilities.
Conclusions:
- The customized fetal BMI percentile model shows excellent, temporally stable discriminative performance, superior calibration, and enhanced clinical utility compared to existing methods.
- The cFBMI model's integration of body proportionality aligns conceptually with the Ponderal Index gold standard.
- Further external multicenter validation and assessment against independent clinical outcomes are recommended before widespread clinical implementation.
