Magnesium sulfate non-specifically and competitively
displaces calcium from the voltage-dependent
calcium channels of myometrial cell membranes
(Figure 4). A Cochrane meta-analysis of 23 trials on
a total of 2036 patients failed to document efficacy
for the prolongation of pregnancy by 48 hours, to the
end of GW 34, or to the end of GW 37 (30). The
meta-analysis did, however, reveal a 2.82-fold
elevation of perinatal mortality when high-dose
magnesium sulfate was given for more than 24
hours. It was concluded that magnesium sulfate cannot
be recommended as a treatment for premature
labor because of its lack of tocolytic efficacy,
increased perinatal mortality, and considerable
maternal side effects (1, 5).