During the first three days of life newborns exhibit a decrease in serum ionized calcium level (Ca++).1 A pathological exacerbation of this process may occur in premature infants, infants born to mothers who are diabetic, and sick infants of any gestational age who were asphyxiated and required active resuscitation.1-6 Thus, approximately 35% of all neonates who require special care will manifest hypocalcemia. Many causes have been suggested for the early neonatal hypocalcemia in these groups of infants, including the following: functional hypoparathyroidism,1,3-5 end-organ unresponsiveness to parathyroid hormone (PTH),7 hypercalcitoninemia,8,9 abnormalities in vitamin D metabolism,10-12 hyperphosphatemia,13 hypomagnesemia,1,13 correction of acidosis,6 and decreased calcium intake and absorption.14
There is an active placental pump of calcium from the maternal to the fetal circulation that results in a relatively hypercalcemic fetus.15 Fetal PTH level is usually low or undetectable,1,3 and PTH does
Fleischman AR, Rosen JF, Nathenson G. 25-Hydroxyvitamin DSerum Levels and Oral Administration of Calcifediol in Neonates. Arch Intern Med. 1978;138(Suppl_5):869–873. doi:10.1001/archinte.1978.03630300037008
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