Magnesium sulfate (MgSO4) is one of the most important and most potentially dangerous medications in obstetric care. It is used for several distinct purposes: seizure prophylaxis in severe preeclampsia, treatment of active seizures in eclampsia, and neuroprotection for the premature fetus under 32 weeks at risk for cerebral palsy; it has also been used as a tocolytic. Because it carries a narrow therapeutic window, the same drug that prevents life-threatening seizures can cause respiratory and cardiac arrest if it accumulates to toxic levels. For this reason, magnesium therapy is a recurring high-yield safety topic on nursing examinations. A foundational concept the nurse must internalize is that magnesium sulfate does not lower blood pressure and is not an antihypertensive. Its role is to prevent and treat seizures by stabilizing neuronal membranes and blocking NMDA glutamate receptors, thereby interrupting the cerebral irritability that leads to eclamptic convulsions. Hypertension in preeclampsia is managed separately with antihypertensive agents such as hydralazine, labetalol, or nifedipine. Confusing these two goals is a classic exam trap. Safe magnesium administration rests on three pillars: continuous physiologic monitoring (deep...