Cerebral Osmolytes and Plasma Osmolality in Pregnancy and Preeclampsia: A Proton Magnetic Resonance Spectroscopy Study

BACKGROUND Cerebral complications contribute substantially to mortality in preeclampsia. Pregnancy calls for extensive maternal adaptations, some associated with increased propensity for seizures, but the pathophysiology behind the eclamptic seizures is not fully understood. Plasma osmolality and sodium levels are lowered in pregnancy. This could result in extrusion of cerebral organic osmolytes, including the excitatory neurotransmitter glutamate, but this remains to be determined. The hypothesis of this study was that cerebral levels of organic osmolytes are decreased during pregnancy, and that this decrease is even more pronounced in women with preeclampsia. METHODS We used proton magnetic resonance spectroscopy to compare levels of cerebral organic osmolytes, in women with preeclampsia (n = 30), normal pregnancy (n = 32), and nonpregnant controls (n = 16). Cerebral levels of organic osmolytes were further correlated to plasma osmolality and plasma levels of glutamate and sodium. RESULTS Compared to nonpregnant women, women with normal pregnancy and preeclampsia had lower levels of the cerebral osmolytes, myo-inositol, choline and creatine (P = 0.001 or less), and all these metabolites correlated with each other (P < 0.05). Women with normal pregnancies and preeclampsia had similar levels of osmolytes, except for glutamate, which was significantly lower in preeclampsia. Cerebral and plasma glutamate levels were negatively correlated with each other (P < 0.008), and myo-inositol, choline and creatine levels were all positively correlated with both plasma osmolality and sodium levels (P < 0.05). CONCLUSIONS Our results indicate that pregnancy is associated with extrusion of cerebral organic osmolytes. This includes the excitatory neurotransmitter glutamate, which may be involved in the pathophysiology of seizures in preeclampsia.