Plasma ionized calcium, phosphate and magnesium in preterm and small for gestational age infants.

Blood concentrations of ionized calcium, phosphate and magnesium were determined on days 1, 3 and 5 in 32 preterm infants, appropriate for gestational age, and 25 small for gestational age infants. The results were compared with those of a reference group of 31 fullterm newborns. Preterm infants had lower mean ionized calcium levels than the reference population. Ionized calcium levels were positively correlated with gestational age and postnatal age. The sickest infants had the lowest calcium levels. Intrauterine growth retardation did not seem to influence the calcium levels. Small for gestational age infants had lower phosphate values than the reference group and the values correlated with the degree of growth retardation the first day. Magnesium concentrations increased with time and did not differ significantly between the study groups and the reference group. Magnesium values did not correlate with calcium or phosphate values.