Factors affecting maternal serum magnesium levels during long-term magnesium sulfate tocolysis in singleton and twin pregnancy

The effects of maternal body mass index and plurality on maternal and umbilical cord serum magnesium levels in preterm birth at less than 32 weeks of gestation

OBJECTIVE

To evaluate the effects of maternal body mass index (BMI) and plurality on maternal and umbilical cord serum magnesium levels after antenatal magnesium sulfate treatment.

METHODS

This was a retrospective cohort analysis of 135 women treated with antenatal magnesium sulfate at less than 32 weeks of gestation between January 2012 and June 2018. Subjects were stratified into groups according to maternal BMI (group I [18.5-22.9 kg/m²], group II [23.0-24.9 kg/m²], and group III [≥25.0 kg/m²]) and plurality (singleton and twin). Univariable and multivariable analyses were performed to compare the umbilical cord serum magnesium levels between the groups.

RESULTS

Maternal serum magnesium levels were not significantly different between the maternal BMI groups and singleton and twin pregnancies. Umbilical cord serum magnesium levels were significantly different among the maternal BMI groups (3.3±1.2 mg/dL in group I, 3.3±1.2 mg/dL in group II, and 4.0±1.4 mg/dL in group III, P=0.003). The trend of increase in magnesium levels was statistically significant (P=0.001, Jonckheere-Terpstra test). Umbilical cord serum magnesium levels were not significantly different according to plurality. However, in the multivariable analysis, maternal BMI and plurality were not significantly associated with umbilical cord serum magnesium levels after adjusting for indication and total dose of magnesium sulfate treatment, gestational age at delivery, mode of delivery, neonatal sex, and birth weight.

CONCLUSION

Maternal BMI and plurality were not significantly associated with maternal or umbilical cord serum magnesium levels after exposure to antenatal magnesium sulfate treatment.

Mechanisms of the effect of magnesium salts in preeclampsia

Preeclampsia is a heterogeneous pregnancy-specific syndrome associated with abnormal trophoblast invasion and endothelial dysfunction. Magnesium (Mg²⁺) level may be normal or decreased in women with preeclampsia. However, the use of Mg²⁺ salts, such as Mg²⁺ sulphate, are useful in reducing the pathophysiological consequences of preeclampsia with severe features and eclampsia. Although the mechanism of action of this Mg²⁺ salt is not well understood, the available evidence suggests a beneficial effect of Mg²⁺ for the mother and foetus. The mechanisms include a lower level of soluble fms-like tyrosine kinase 1 and endoglin, blockage of brain N-methyl-D-aspartate receptors, decreased inflammation mediators, activation of nitric oxide synthases, blockage of arginases, and reduced free radicals level. The maintenance of Mg²⁺ homeostasis in pregnancy is crucial for an appropriate pregnancy progression. Oral Mg²⁺ salts can be used for this purpose which could result in mitigating the deleterious consequences of this syndrome to the mother, foetus, and newborn.