Serum ionized magnesium during magnesium sulfate administration for preterm labor and preeclampsia.

Objective: The purpose of this study is to estimate the relations between ionized and total Mg levels during MgSO4 administration in patients with preterm labor and preeclampsia.

Methods: Forty-three pregnant patients who were candidates for MgSO4 were studied (preterm labor, 27; preeclampsia, 16). The administration method was intravenous injection of MgSO4 4 g over 30 min followed by 1-2 g/h. Ionized Mg was measured by the selective ion electrode method at bedside, and compared it with total Mg levels.

Results: Significant correlation was existed between levels of ionized and total Mg throughout therapy for both preterm labor (ionized Mg=0.19 x total Mg+0.19; r=0.61, p<0.001) and preeclampsia (ionized Mg=0.20 x total Mg+0.14; r=0.60, p<0.001).

Conclusion: There are correlations between ionized and total Mg levels during administration of MgSO4 for both preterm labor and preeclampsia.