A Model to Define Reference Ultrasound Parameters for Early Assessment of Nephron Endowment in Extremely Low Birth Weight Preterm Infants

Background: Preterm birth, the leading cause of neonatal mortality, is associated with reduced nephron endowment and an increased risk of kidney disease in later life. In preterm infants, the interruption of nephrogenesis leads to a lower nephron number and structural abnormalities. Prenatal factors such as intrauterine growth restriction, and postnatal factors including nephrotoxic medications, patent ductus arteriosus, perinatal asphyxia, and infections contribute to this deficit. Ultrasound is a key tool for assessing renal volume at birth and can, when indexed to body weight, be used to estimate nephron endowment, which is known to vary widely among individuals. Methods: This study analyzed 52 preterm infants with birth weight < 1000 g, assessing combined renal volume (sum of right and left kidney volumes) indexed to body weight. Results: The mean combined kidney volume-to-body weight ratio was 12.12 (SD = 2.03). Values below the 10th percentile (9.46) or more than one standard deviation below the mean (10.11) may indicate nephron deficiency at birth. Conclusions: Standardized ultrasound-based parameters enable the early identification of neonates at risk for nephron deficit, supporting targeted preventive strategies. Long-term follow-up is essential to detect early renal functional impairment and reduce the risk of chronic kidney disease.