Perinatal serum bone Gla-protein and vitamin D metabolites in preterm and fullterm neonates.

Whether the hypocalcemia often found in premature neonates results from an adaptation to extrauterine life or an expression of imbalanced mineral homeostasis has yet to be established. We compared serum levels of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D [1,25-(OH)2D], and bone Gla-protein (BGP), a specific marker of bone formation during the first month of life in fullterm and preterm neonates. Measurements were performed in cord blood and on days 1, 5, and 30 of life. In maternal blood, mean serum 1,25-(OH)2D concentrations were higher in the mothers of premature than in those of fullterm neonates, and serum BGP concentrations were lower than those in nonpregnant women. In cord blood mean serum BGP levels were 2-3 times higher than in adults. Serum BGP increased significantly on days 5 and 30 in fullterm infants. In preterm infants, and increase was found only on day 30. Mean serum 25-hydroxyvitamin D and 1,25-(OH)2D concentrations were lower in neonates than in mothers, but not different in fullterm and preterm neonates. In fullterm infants serum 1,25-(OH)2D increased rapidly from birth to day 5 and decreased on day 30. The pattern was similar in preterm infants, but 1,25-(OH)2D was higher than in fullterm infants on day 30. No sustained correlation between serum BGP and 1,25-(OH)2D levels was found. These data support the contention that changes in 1,25-(OH)2D reflect the perinatal equilibration of calcium homeostasis. Serum BGP may be a potential marker of bone growth in premature neonates.