Bone turnover markers and bone strength during the first weeks of life in very low birth weight premature infants

Objective: To determine the association between changes in bone turnover markers and bone strength of very low birth weight infants during the first eight postnatal weeks. Study design: Twelve very low birth weight premature infants [mean gestational age: 28.4±0.6 weeks, mean birth weight: 1131±62 grams] participated in the study. Bone strength was evaluated weekly by quantitative ultrasound measurements of tibial bone speed of sound (SOS, Sunlight Omnisense™). Bone specific alkaline phosphatase (BSAP), a marker of bone formation, and carboxy terminal cross-links telopeptide of type-I collagen (ICTP), a marker of bone resorption, were collected at the ages of one, four and eight weeks. Results: BSAP increased significantly (from 119.9±16.2 U/L to 132.1±11.9 U/L and 152.1±15.7 U/L at one, four and eight weeks of life, respectively, p<0.05). ICTP decreased significantly during the study period (from 122.3±8.7 ng/ml to 96.0±4.8 ng/ml and 92.3±5.4 ng/ml at one, four and eight weeks of life, respectively; p<0.05). There was a significant decrease in bone SOS (from 2886±29 m/sec to 2792±30 m/sec and 2753±30 m/sec at birth, four weeks and eight weeks of life, respectively; p<0.02). There was no correlation between the levels of bone markers and bone SOS Conclusion: In VLBW premature infants, there is a significant decrease in bone strength concomitant with biochemical evidence for new bone formation (increase in BSAP and a decrease in ICTP) during the first eight postnatal weeks. Changes in the biochemical markers could not predict the changes in bone strength.