Introduction:​ Metabolic bone disease of prematurity (MBD) frequently affects preterm infants. The accurate diagnosis of the MBD remains a challenging issue despite characteristic clinical, laboratory and imaging features. Recently, non-invasive quantitative ultrasound (QUS) measuring speed of sound (SOS) has been applied to assess bone status. Limited data are available on comparison of QUS among preterm infants.

Objective:​ To evaluate development of tibial bone SOS values in preterm infants during the first year of life and compare the SOS values among different birth weight categories.

Methods:​ QUS was used in 153 infants below 34 weeks of gestation. The study group was divided into 3 subgroups based on birth weight (BW):​ ≤1000 g, 1001–1500 g and >1500 g. SOS measurement was performed at 6 and 12 months of corrected age (CA).

Results:​ Overall, we found significant increase in mean tibial SOS between 6 and 12 months of CA (3004 ± 123 vs 3253 ± 109 m/s, p = 0.001). There were significant differences in SOS among birth weight categories at 6 months of CA (p = 0.045). However, these differences were not statistically significant at 12 months of CA (p = 0.289). The infants ≤ 1000 g scored the highest SOS values at both time points.

Conclusions:​ Tibial SOS significantly increases during infancy in preterm newborns. Significant variation exists in SOS at 6 months, but not at 12 months of corrected age according to BW. Moreover, inverse correlation between BW and SOS indicating better bone status was revealed in extremely low birth weight infants at both 6 or at 12 months of CA.