Organ size in small infants (The OSSI Study): are sonographic reference intervals applicable in preterm infants small for gestational age?

Sonographic reference intervals for liver, spleen, and kidney size in preterm infants below 40 cm body length were recently established in an appropriately grown (AGA) neonatal cohort. Whether these intervals apply to infants born small for gestational age (SGA) remains unexamined. In this cross-sectional study, 20 preterm SGA infants below 40 cm body length (mean gestational age 29 ¹/₇ weeks, median birth weight 695 g) underwent standardized abdominal ultrasound, measuring craniocaudal liver length in three planes, splenic length, and renal volume. Measurements were compared with published reference intervals, and z-scores assessed systematic deviation. Weight and length at examination were comparable between the SGA and AGA cohorts. The mean z-score was significantly below zero only for liver length in the midclavicular line (- 0.79, p = 0.014). The proportion of infants outside the reference interval exceeded the expected 5% for liver length in the midclavicular line (25%, p = 0.003) and anterior axillary line (20%, p = 0.016) and for spleen length (20%, p = 0.016), but rested on 4 to 5 infants each, and several values lay within 1 mm of the limit. Kidney measurements did not differ from the reference. Organ size correlated most strongly with body weight, and the deviations persisted at equal weight (post hoc).

Abdominal organ dimensions in SGA preterm infants frequently fall outside AGA-derived reference intervals, particularly for liver and spleen size, suggesting that these intervals cannot be reliably applied to this population. Prospective studies establishing reference values for SGA infants are warranted.

• Sonographic reference intervals for abdominal organ size in preterm infants below 40 cm exist only for appropriately grown (AGA) infants; their applicability to infants small for gestational age (SGA) has not been examined.

• In 20 preterm SGA infants, the mean z-score for liver length (midclavicular line) was below the AGA reference, and liver and spleen lengths fell outside the intervals more often than the expected 5% (exploratory). • AGA intervals should not be assumed to apply to SGA infants.