Data from trials never clearly demonstrated that magnesium has a clinically significant tocolytic effect compared with “control” treatments. In a Cochrane review of magnesium tocolysis, neither improvement in the risk of delivery before 48 hours nor reduction in risk of birth before 34 or 37 weeks was observed, compared with control treatments. More recent data also suggest that magnesium may increase the risk of adverse neonatal outcomes, including death, especially at the upper end of the magnesium dose range.
In the absence of demonstrated clinical efficacy and a concern over potentially negative neonatal effects, obstetricians should consider strictly limiting their use of magnesium for tocolysis.
Link: Is the end of an era here for magnesium sulfate tocolysis?