SERUM MAGNESIUM LEVELS DURING MAGNESIUM-SULFATE TOCOLYSIS IN HIGH-ORDER MULTIPLE GESTATIONS

The objective of this study tons to determine the serum levels of magn esium associated with various intravenous infusion rates of magnesium sulfate (MgSO4) in high-order multiple gestations. A retrospective rev iew of 12 triplet and 4 quadruplet pregnancies caved for in Phoenix fr om August 1988 to January 1992 was performed. The mothers received MgS O4 for tocolysis of preterm labor. Serum magnesium levels were drawn t o help manage patients with symptoms of an excessive magnesium level o r an inadequate tocolytic effect. The results are presented for triple ts and quadruplets with and without pregnancy-induced hypertension (PI H). The serum levels of Mg++ in triplets and quadruplets were similar to those in singleton pregnancies described in the literature. Higher serum levels of Mg++ (7.0-7.5 mg/dL) seemed to be necessary for succes sful tocolysis. Serum levels of Mg++ in patients with underlying PIH w ere significantly higher at the same intravenous infusion rate. MgSO4 may need to be administered at infusion rates of 4-5 g/h to achieve th erapeutic levels in women with triplets and quadruplets. PIH should re quire lower infusion rates to achieve therapeutic ic serum levels of M g++.