To assess longitudinal changes in speed of sound (SOS) in very low birth weight (VLBW) infants and investigate the relationship with markers of osteopathy of prematurity (OP) and clinical illness.

Twenty-five infants were recruited. Eighteen infants, median gestation 27 weeks (range 24–32), median birth weight 957 g (range 625–1500 g), had serial scans. SOS was measured at both tibiae weekly until 35 to 37 weeks corrected gestational age (CGA).

Initial median SOS standard deviation score (SDS) (Z) score was −0.07 (range −1.3–1.3). SOS correlated with gestation (r, 0.8, P <.005), and birth weight (r, 0.67, P <.005.) SOS fell from a median of 2923 m/s (2672–3107) at birth to 2802 m/s (2502–2991) at 35 to 37 weeks CGA (P <.05). This fall was greater in the 24- to 27-week gestation cohort with a median reduction of 2.2 SDS (1.6, 4.0) compared with 1.3 SDS (0.8–2.2) in those >28 weeks (P <.05). There was a negative correlation between SOS, at the end of the study, peak serum alkaline phosphatase (ALP) (r, 0.6, P <.05), CRIB (Clinical Risk Index for Babies)/CRIB II scores (both r, 0.6, P <.05), and duration of total parenteral nutrition (TPN) (r, 0.58, P <.05.)

Although tibial SOS was within the expected range at birth, there was a subsequent failure to gain SOS, and this was most marked in infants of a lower gestation.