Correlation between magnesium sulphate exposure in utero and serum calcium and alkaline phosphatase levels in preterm infants

Introduction: Magnesium sulphate (MgSO4) is administered to pregnant women at risk of preterm labour and eclampsia. Since prolonged exposure to antenatal MgSO4 is considered to be a risk factor for infant skeletal demineralization, we evaluated infants exposed to antenatal MgSO4 for bone and mineral metabolism using their umbilical cord blood.

Materials and methods: The study population comprised 137 preterm infants. Forty-three infants were exposed (exposure group) and 94 infants were not exposed (control group) to antenatal MgSO4. Blood samples from the umbilical cords and infants were analysed with respect to mineral metabolism, intact parathyroid hormone (iPTH) level, and alkaline phosphatase (ALP) level. Correlation between the level of these parameters and the duration and dosage of MgSO4 was also examined.

Results: Preterm infants in the exposure group were antenatally exposed to MgSO4 for a median (IQR) period of 14 (5-34) days and a dosage of 447 (138-1118) g. Serum calcium levels were lower (8.8 vs 9.4 mg/dL, p<0.001) and ALP levels were higher (312 vs 196 U/L, p<0.001) in the exposure group. Serum calcium levels did not correlate with MgSO4 administration dosage and therapy duration, however, ALP levels correlated with the duration and total dosage of MgSO4 (Spearman's rank correlation r [95% confidence interval]: 0.55 [0.30-0.73], p <0.001 and 0.63 [0.40-0.78], p <0.001, respectively).

Conclusion: Prolonged periods and higher doses of antenatal MgSO4 exposure can cause in utero abnormal bone metabolism in preterm infants.