Effects of magnesium sulfate treatment on perinatal calcium metabolism. II. Neonatal responses.

To evaluate the effects of maternal magnesium sulfate treatment on neonatal magnesium and calcium homeostasis, the authors studied 23 term neonates whose mothers had received intravenous magnesium sulfate for pre-eclampsia and compared them with 14 control neonates. Total and ionized calcium, magnesium, phosphorus, and albumin were measured in maternal and umbilical blood; total calcium, magnesium, phosphorus, and albumin were measured serially in the newborn infants. Magnesium levels were higher in treated than in control infants in umbilical venous and arterial blood samples and in the neonatal blood samples 2, 12, and 24 hours after delivery. However, at 48 hours and beyond there was no difference in serum magnesium levels between treated infants and controls. Calcium levels were not significantly different in treated versus control subjects in umbilical blood or in any neonatal samples. There was no correlation between the maternal magnesium concentration at delivery and the levels of calcium in umbilical or neonatal blood. These data indicate that maternal magnesium sulfate therapy does not cause neonatal hypocalcemia and that the induced neonatal hypermagnesemia is resolved within the first 48 hours of life.