A nurse is preparing to administer magnesium sulfate IV to a client who is experiencing preterm labor. Which of the following is the priority nursing assessment for this client?

A. Fetal heart rate (FHR): While FHR monitoring is essential in any obstetric situation, magnesium sulfate is a central nervous system (CNS) depressant. The immediate life-threatening risk to the mother (which would secondarily affect the fetus) is respiratory arrest. B. Temperature: Magnesium sulfate can cause flushing and feelings of warmth, but it does not typically cause significant fever or hypothermia that would make temperature the priority assessment. C. Respiratory rate: Magnesium sulfate is a high-alert medication used to stop preterm labor (tocolytic) and prevent seizures in preeclampsia. Its primary mechanism is CNS depression. Toxicity leads to respiratory depression, loss of deep tendon reflexes (DTRs), and cardiac arrest. If the respiratory rate drops below 12/min, the medication must be stopped immediately. D. Bowel sounds: While magnesium can cause smooth muscle relaxation (potentially leading to constipation or ileus), this is not a life-threatening priority compared to airway and breathing.