Organ size in small infants (The OSSI Study): establishing sonographic reference intervals for abdominal organs in preterm infants

Abstract Accurate ultrasound assessment of abdominal organ size in preterm infants is essential for evaluating growth and detecting abnormalities. However, standardized reference intervals for liver, spleen, and kidney dimensions in preterms below 40 cm body length are lacking. This study aimed to establish reference intervals for these organs. 57 eutrophic preterm infants with a body length below 40 cm (gestational age: 23 4 / 7 —31 5 / 7 weeks; birth length: 29—39.5 cm) were prospectively examined using a standardized ultrasound protocol recommended by the German Society for Ultrasound in Medicine (DEGUM). Craniocaudal liver length, spleen length, and renal volume were measured and correlated with corrected gestational age, body weight, and body length. Reference intervals were calculated from log-transformed data with 95% confidence intervals for reference limits. Portal vein peak velocity before feeding and presence of a patent ductus venosus (PDV) were additionally assessed. Organ dimensions correlated most closely with body weight, followed by body length and corrected gestational age, with renal volume showing the highest correlations overall. Reference intervals for liver, spleen, and renal size showed tight 95% confidence intervals. Portal vein peak velocity ranged from 9—29 cm/s. A PDV was present in 56%; these infants were younger at examination (10.9 vs. 17 days, p = 0.01). Conclusion : This study provides clinically relevant ultrasound reference intervals for abdominal organs in small preterm infants. These measurements may help distinguish physiological from pathological findings and guide clinical decision-making in neonatal care. What is Known: • Ultrasound is the preferred imaging modality for abdominal organ assessment in preterm infants, but standardized sonographic reference intervals for infants with a body length below 40 cm are lacking. What is New: • This study provides the first standardized sonographic reference intervals for liver length, splenic length, and renal volume in preterm infants below 40 cm body length, using a prospective, reproducible protocol aligned with DEGUM recommendations. • Organ size correlated most strongly with body weight, followed by body length and corrected gestational age, with renal volume showing the highest overall correlations across all parameters.