Focus On Maternity Practice Exam

Magnesium sulfate in preeclampsia is used to prevent seizures by raising the brain’s seizure threshold and dampening neuromuscular excitability, acting as a central nervous system depressant to reduce the risk of progression to eclampsia. It may also cause mild vasodilation that can help with uteroplacental blood flow, but the primary purpose is seizure prophylaxis. Toxicity signs reflect excessive CNS and neuromuscular suppression. Early warning is loss or depression of deep tendon reflexes; as toxicity worsens, respirations may slow to fewer than about 12 breaths per minute, urine output may drop below 30 mL per hour, and the patient can become drowsy, confused, or have altered consciousness. If toxicity is suspected, stop the infusion and administer calcium gluconate as the antidote. Other options don’t fit the main purpose of magnesium sulfate. It isn’t given primarily to lower blood pressure, promote placental separation, or accelerate fetal lung maturity (the latter is achieved with antenatal corticosteroids).