Objective: Our aim was to test the hypothesis that maternofetal placental calcium transfer rate decreases in experimentally induced acute maternal hypermagnesemia in the rat.
Study design: We measured the unidirectional maternofetal clearance of calcium 45 and chromium 51-ethylenediaminetetraacetic acid across in situ perfused placentas of rats randomized to intravenous treatment with saline solution and magnesium sulfate (n = 5) or to saline solution only (n = 5) before placental perfusion. The maternofetal clearance of chromium 51-ethylenediaminetetraacetic acid provides a measure of placental "porosity" or passive permeability.
Results: The mean serum magnesium concentration increased to 5.3 +/- 0.6 mg/dl (2.18 +/- 0.25 mmol/L) in magnesium-infused rats, staying at 1.8 +/- 0.1 mg/dl (0.74 +/- 0.04 mmol/L) in control rats (p < 0.001). Neither the maternofetal clearance of calcium 45 nor that of chromium 51-ethylenediaminetetraacetic acid was affected by acute maternal hypermagnesemia.
Conclusion: Within the range of hypermagnesemia studied, placental calcium transport remains unaffected.