Bone Growth with Low Bone Mineral Content in Very Low Birth Weight Premature Infants

Abstract

We report serial measurements of bone mineral content (BMC), bone width (BW, a measure of appositional bone growth), and the ratio of BMC:BW by photon absorptiometry of the left radius through the first 10 wk of life in 38 very low birth weight premature infants (birth weight <1300 g, gestational age <32 wk). Fifteen of 38 infants developed bronchopulmonary dysplasia (BPD) and as a group they could not be distinguished from the 23 infants without BPD, despite the high association between BPD and metabolic bone disease. As BPD occurred in the smaller patients, the BPD group had a significantly lower mean birth weight and mean gestational age as compared to controls (950 ± 125 g versus 1119 ± 149, and 28.0 ± 0.8 versus 29.0 ±1.3 wk). For both control and BPD groups, BMCs did not differ and remained relatively unchanged throughout the first 10 wk of life, lagging significantly behind the intrauterine rate as defined by measuring BMC in 175 infants of varying gestational ages during the first few days of life. BW also did not differ during this period between groups. BW did increase significantly in both groups (from 3.2 ± 0.3 to 3.9 ± 0.4 mm in the controls and from 3.0 ± 0.3 to 3.8 ± 0.4 mm in the BPD group), but remained significantly delayed compared to the intrauterine rate. In both groups, BMC remained relatively constant despite increasing BW and thus BMC/BW decreased during the first 10 wk of life (from 11.5 ± 1.3 to 10.2 ± 1.9 in the controls and from 11.0 ± 1.3 to 8.6 ± 2.2 in the BPD group). Thus in very low birth weight infants, with and without BPD, we have clearly documented a decrease in BMC compared to the intrauterine values. This occurs despite appositional and overall skeletal growth, indicating a disorder of formation and/or remodeling of growing cortical bone.