Correlation of Total Dosage and Duration of Magnesium Sulfate Administration in Pregnant Women Associated with Magnesium Levels in Umbilical Cord Blood
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Abstract
Objectives: To evaluate the correlation between the total dosage and duration of maternal magnesium sulfate (MgSO4) administration and umbilical cord blood magnesium levels, and to determine clinically useful cutoff values associated with elevated neonatal magnesium concentrations.
Materials and Methods: The cross-sectional study included 47 pregnant women ≥ 24 weeks’ gestation who received MgSO4 following the regimen of loading dose 4 grams, followed by a maintenance dose of 2 gram/hour intravenously at Rajavithi Hospital. Maternal serum magnesium was collected within 1 hour before delivery, and umbilical cord blood samples were obtained immediately after placenta delivery. Total MgSO4 dose, infusion duration, and biochemical parameters were recorded. Pearson’s correlation, linear regression, and receiver operating characteristic (ROC) curve analysis were performed.
Results: Total dosage of MgSO4 and infusion duration showed significant positive correlations with cord blood magnesium levels (r = 0.65, p < 0.001). Maternal serum magnesium demonstrated the strongest correlation (r = 0.73, p < 0.001) and remained an independent predictor in the multivariable model together with maternal serum creatinine. ROC analysis identified two clinically useful cutoff values for predicting cord magnesium ≥ 5 mg/dL: a total dose of 12.8 g (sensitivity 100%, specificity 71.4%) and an infusion duration of 280 minutes (sensitivity 100%, specificity 68.6%). A higher level of exposure, corresponding to 31.3 g of total dose or 855 minutes of infusion, yielded 100% specificity.
Conclusion: Both the total dosage of MgSO4 and infusion duration were strong predictors of neonatal cord blood magnesium levels. The identified cutoff values provided practical guidance for assessing the risk of elevated neonatal magnesium exposure and support targeted newborn surveillance following maternal MgSO4 therapy.
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