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MATERIALS AND METHODSand BW at birth. Because ofthe direct relationship between BMC and BW we speculated that the ratio of BMC to BW would be useful in identifying disorders of bone mineral metabolism in low birth weight infants (I).In the present study, we report serial measurements of BMC and BW through the first 10 wk of life in 38 VLBW premature infants. We hypothesized that during this period of active growth in weight and length, BW (a measure ofbone diameter and hence of appositional bone growth in infancy and childhood) would increase secondary to increased matrix formation (2); however, we predicted BMC would decrease or remain unchanged due to insufficient mineral intake compared to that necessary to achieve the intrauterine rate of bone mineralization (l). Following entry into the study, 15 of 38 infants developed BPD and we hypothesized that as a group they could be distinguished from the 23 infants without BPD because of the high association between BPD and metabolic bone disease (3). We anticipated that the ratio of BMC to BW would be lower in the BPD group compared to controls.Population. Thirty-eight VLBW infants (birth weight < 1300 g, gestational age <32 wk) were recruited for this study during the 1st wk of life, after obtaining parental informed consent. Thirty-five infants were white and three infants were black. All infants were appropriate for gestational age. Gestational age was determined from the history of the last menstrual period and corroborated by the Ballard examination for those infants greater than 27 wk gestational age (4). For those infants less than or equal to 27 wk gestation, fetal ultrasound measurements were used as the second corroborator ofgestational age, when available from the department of obstetrics. If there was more than a 2-wk discrepancy between the two determinations of gestational age, the infant was excluded from the study. All infants were admitted to the neonatal intensive care unit at Madison General Hospital and all were free from major congenital malformations.Of these 38 infants, 15 were diagnosed subsequently as having BPD. All infants with BPD had the initial diagnosis of the respiratory distress syndrome, required supplemental oxygen for a minimum of 30 days, and had a chest x-ray diagnosis of BPD (hyperexpansion, interstitial densities, focal emphysema) (5). For purposes of comparison, the remaining 23 infants were designated as controls.Photon absorptiometry. BMC and bone width were measured by a photon absorptiometric system (Lunar Radiation Inc., Madison, WI) in which a collimated 2 mm diameter photon beam from a low activity [ 125 1] "spent source" (20-50 mCi) was passed beneath the one-third distal radius (shaft) of the left forearm. The system has been previously described in detail (1). Measurements of BMC and bone width were made within the 1st wk of life and subsequently at biweekly intervals. Accuracy, precision, and reproducibility of this system used by us in newborn infants have been published (1). Immediate reproducibility 925 Abbrevi...

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