Diagnostic accuracy of newborn foot length measurement in identifying low birth weight and preterm infants in Sidama Region, Ethiopia

Belay, F.W. and Belayneh, F.B. and Alemayehu, A. and Fikre, R. and Clarke, A. and Williams, S. and Richards, H. (2025) Diagnostic accuracy of newborn foot length measurement in identifying low birth weight and preterm infants in Sidama Region, Ethiopia. BMJ Paediatrics Open, 9 (1): e003374. ISSN 2399-9772

Abstract

Background Low birth weight (LBW) and preterm birth significantly contribute to increased risks of neonatal mortality, particularly in sub-Saharan Africa. Early identification of and timely intervention for these vulnerable infants remains challenging. Simple anthropometric measurements, such as foot length (FL), have emerged as potential alternatives to identify small and vulnerable newborns. This study aims to assess the accuracy of FL as a screening tool to identify LBW and preterm babies and to establish appropriate cut-off points for the local context. Methods A facility-based cross-sectional study was conducted at Hawassa University Comprehensive Specialised Hospital and Bushulo Mother, Newborn and Child Health Specialty Centre and Primary healthcare from 15 May 2024 to 6 July 2024; 396 mother-newborn dyads were included using a consecutive sampling technique. Data were collected through interview, medical record review and FL measurement using digital calliper. Birth weight was measured using calibrated digital weight scales. Descriptive statistics, correlation analysis and receiver operating characteristic (ROC) curves were used to assess the distribution of measured characteristics and determine optimal FL cut-off points for identifying LBW and preterm babies. Results The study included 61 (15.4%) LBW and 48 (12.3%) preterm babies. FL showed a strong correlation with birth weight (r=0.79) and moderate correlation with gestational age (r=0.62). The optimal cut-off point for identifying LBW babies was 70.65mm, yielding 93.4% sensitivity, 91.6% specificity and an area under receiver operator curve (AUC) of 0.97 (95% CI: 0.95 to 0.98). For preterm babies, the optimal cut-off was 69.95mm, with 76.7% sensitivity, 91.1% specificity and an AUC of 0.91 (95% CI: 0.86 to 0.96). Conclusion FL has demonstrated excellent diagnostic accuracy to identify LBW and preterm newborns. Optimal accuracy of identifying LBW and preterm babies in similar populations can be achieved at 70.65 and 69.95mm cut-off points, respectively. In designing FL-based screening tools, appropriate cut-off points for the required level of accuracy should be considered.