Association between magnesium, calcium, phosphorus, copper, and zinc in umbilical cord plasma and erythrocytes, and the gestational age and growth variables of full-term newborns.

We determined reference values in umbilical cord plasma and erythrocytes for magnesium, total calcium, phosphorus, copper, and zinc, and then calculated correlations and stepwise-regression equations in 66 white full-term newborn infants (35 boys, 31 girls). Only infants meeting certain optimal criteria and benefiting from excellent maternal conditions and uncomplicated pregnancies were included. There were no significant sex-related differences at birth among the variables studied. Gestational age was positively correlated with erythrocyte zinc (P less than 0.001), and plasma calcium was positively correlated with erythrocyte copper (P less than 0.001). Plasma copper proved to be the most significant variable in the stepwise-regression equation for birth height as the dependent variable. The most significant regressors accounting for birth weight were erythrocyte zinc followed by plasma zinc.