Disparity in post-treatment maternal circulating magnesium sulfate levels between twin and singleton gestation: Is this the missing link between plurality and adverse outcome?

Magnesium sulfate (MgSO₄) administered to women at risk for preterm delivery decreases the risk of cerebral palsy in their children. However, the neuroprotective effect of MgSO₄ has not been shown in twin gestations. Thus, the aim of this study was to determine the maternal serum levels of magnesium in twin vs. singleton pregnancies following intravenous treatment of MgSO₄. Methods: Case control study including two groups of pregnant women who received intravenous MgSO₄: (1) twin gestations (n=83) and (2) singleton pregnancies (n=83). Maternal serum magnesium levels 6 and 24 h after initiation of treatment were determined in both groups. Results: Maternal serum levels of magnesium were significantly lower among patients with twin gestations compared to those with singleton ones 6 h after initiation of treatment (4.6 vs. 4.8 mg/dL, P=0.003). In addition, the rate of pregnant women who obtained therapeutic levels 6 h after initiation of treatment was significantly lower in twin gestations than in singleton ones (36% vs. 58%, P=0.008). Multiple regression analysis revealed that twin gestations were independently and significantly associated with low maternal serum magnesium levels. Conclusions: Maternal serum concentrations of magnesium are lower in twin pregnancies than in singleton ones following MgSO₄ treatment, which might explain the decreased neuroprotective effect of MgSO₄ reported in twin pregnancies.