Maternal–fetal effects of magnesium sulfate on serum osmolality in pre-eclampsia

Abstract

Objective: To determine the effects of magnesium sulfate therapy on maternal and fetal osmolality in pre-eclampsia.Methods: A total of 34 pre-eclamptic women and 22 normal pregnant womenparticipated in the study. Venous blood was drawn upon admission to the labor and delivery unit. Pre-eclamptic patients received standard magnesium sulfate therapy and had a second sample of venous blooddrawn 4 h following the beginning of therapy. Fetal umbilical vein blood was obtained immediately following delivery in both groups. Osmolality was measured using a vapor pressure osmometer. Electrolytelevels were measured with a NOVA 8 biomedical analyzer. Data were analyzed via Student's t test, linear regression and correlation with significance established at p < 0.05.Results:We found no significant difference between the maternal osmolalities of the control and pre-eclamptic groups. Interestingly, fetal cord blood osmolality was significantly lower than maternal osmolalityin the normal pregnant women. Sodium levels were also lower, while potassium and ionized calcium levels were higher in the fetal blood. In women with pre-eclampsia treated with magnesium sulfate, therewas no difference between the osmolality of the maternal and fetal blood, while potassium and ionized calcium levels were still higher in the fetal blood. Finally, we found no correlation between maternalosmolality and blood pressure.Conclusions: High blood pressure in pre-eclampsia is not associated with altered osmolality. An absence of the normal decrease in fetal osmolality is observed inpre-eclamptic women treated with magnesium sulfate.