Maternal magnesium therapy, neonatal serum magnesium concentration and immediate neonatal outcomes

The fetus is exposed to magnesium administered to the pregnant mother. However, there is controversy regarding magnesium-related neonatal adverse outcomes, largely driven by a limited understanding of the factors that influence neonatal serum magnesium concentrations and associated outcomes. The objective of this study was to examine the relationship between antenatal maternal magnesium dose and serum concentrations, neonatal serum magnesium concentration and immediate neonatal outcomes.

A retrospective study was conducted at a community-based teaching hospital. Neonatal serum magnesium concentrations within 48 h of birth were used to stratify magnesium-exposed neonates into three groups: group 1: <2.5 mg dl^-1, group 2: ⩾2.5 to <4.5 mg dl^-1, and group 3:⩾4.5 mg dl^-1. Immediate neonatal outcomes were compared between the three groups. Total maternal magnesium dose and serum magnesium concentrations before the delivery were correlated with neonatal serum magnesium concentrations and outcomes.

Of the 304 mother-baby dyads between 24 and 34 weeks gestation, 237 received antenatal magnesium. Neonatal serum magnesium concentration was 3.14±0.83 mg dl^-1 in exposed and 1.96±0.42 mg dl^-1 in unexposed neonates (P<0.001). Compared with group 2, neonates had higher odds of grade 3 or 4 intraventricular hemorrhage in group 1 (adjusted odds ratio (AOR) 5.95 (95% confidence interval (CI) 1.05 to 33.66)) and group 3 (AOR 8.42 (95% CI 1.35 to 52.54)). Group 3 neonates also had increased odds of periventricular leukomalacia (AOR: 5.37 (95% CI 1.02 to 28.28) compared with group 2 neonates. Predictors of neonatal serum magnesium concentrations included maternal magnesium dose (r=0.66, P<0.0001), duration of therapy (r=0.70, P<0.0001) and serum concentration (r=0.72, P<0.001).

The between-group differences highlight that there is a therapeutic range of neonatal serum magnesium concentrations for neuroprotective effects of antenatal magnesium sulfate, while concentrations outside of this range may be associated with adverse neonatal outcomes. Further studies are needed to determine the optimal dose and duration of maternal magnesium to minimize adverse neonatal outcomes.