Total and ionized serum magnesium and calcium levels during magnesium sulfate administration for preterm labor.

Objective: This study aimed to estimate the association between total and ionized magnesium, and the changes in serum magnesium and calcium levels in patients with preterm labor during magnesium sulfate (MgSO4 ) administration.

Methods: The study population included 64 women who were candidates for intravenous MgSO4 treatment for preterm labor. Serial blood samples were taken and measured total magnesium (T-Mg), ionized magnesium (I-Mg), total calcium (T-Ca), and ionized calcium (I-Ca) levels every one-week interval (1st, 2nd, 3rd).

Results: There was no significant difference in T-Mg and I-Mg levels during MgSO4 administration ( P >0.05). There was no significant difference in T-Ca and I-Ca levels during MgSO4 administration ( P >0.05). Compared before and after administration of MgSO4 , T-Mg and I-Mg levels and T-Ca levels were changed allow statistically significant ( P <0.05). But, there was no significant difference in the I-Ca serum levels before and after MgSO4 administration ( P =0.495). The I-Mg levels for patients with adverse effect were higher than other group but did not reach statistical significance ( P >0.05). There was significant correlation between levels of I-Mg and T-Mg (I-Mg=0.395×T-Mg+0.144, P <0.01).

Conclusion: There were no significant differences in serum Mg and Ca levels during MgSO4 administration for preterm labor. Compared to the before and after administration of MgSO4 , only I-Ca levels were not substantially changed. There are significant correlations between I-Mg and T-Mg levels during administration of MgSO4 and I-Mg level seemed to have more correlation with adverse effect than T-Mg.