Total body bone mineral content in small-for-gestational -age, appropriate-for-gestational -age, large-for-gestational -age term infants and appropriate-for-gestational -age preterm infants.

Background: Metabolic bone disease is a recognized complication in very low birth weight infants. Inadequate postnatal intake of calcium and phosphorus is probably important in the pathogenesis of bone disease in the newborn. A few studies have shown lower bone mineral content at birth in small for gestational age (SGA) than in appropriate for gestational age (AGA) infants. The present study was designed to compare total body bone mineral (TBBM) content in AGA, SGA, and large for gestational age (LGA) term infants. Also, it was designed to evaluate extrauterine changes in TBBM in preterm infants.

Methods: Ten SGA [mean +/- S.D. birth weight (B.W.) was 1.7 +/- 0.2 Kg, gestational age (G.A.), 39.0 +/- 0.8 weeks], ten AGA (B.W.; 3.3 +/- 0.4 Kg; G.A.: 39.3 +/- 1.4 weeks), ten LGA (B.W.: 4.4 +/- 0.3 Kg; G.A.: 40.4 +/- 0.9 weeks) term infants and ten AGA preterm infants (B.W.: 1.6 +/- 0.3 Kg; G.A.: 31.9 +/- 1.9 weeks) were enrolled in this study. TBBM content was measured using dual-photon-absorptiometry at 1 week postnatally in SGA, AGA, LGA term infants and in preterm infants at 1, 6, 12 weeks postnatally. Serum total calcium, phosphorus, magnesium, alkaline phosphatase activity (alk-p), parathyroid hormone (PTH), 25-hydroxyvitamin D (25-OHD) and urinary calcium, phosphorus, creatinine were measured at 1 week postnatally in all studied infants and 6, 12 weeks, postnatally in preterm infants. Preterm and SGA term infants received premature formula enriched with calcium, phosphorus and vitamin D.

Results: There was no significant difference (p > 0.05) in serum calcium, phosphorus, magnesium, alk-p, PTH, 25-OHD and urinary calcium, phosphorus, creatinine values among SGA, AGA and LGA term infants at one week of age. Also, there was no significant difference in serum biochemical values in preterm infants at 1, 6, 12 weeks postnatally. Significantly lower (p < 0.05) urinary phosphorus values were found in preterm than in term infants. TBBM content was lower (p < 0.05) in SGA term infants than in AGA and LGA term infants. Premature infants had lower (p < 0.01) TBBM values than term AGA infants; however, TBBM values increase with postnatal age in preterm infants.

Conclusions: Biochemical or marked radiological evidence of metabolic bone disease did not develop in any of the studied preterm infants. It appears that feeding permature infants with formula enriched with phosphorus, calcium and vitamin D may provide sufficient mineral for bone mineralization.