OBJECTIVE: To use individual patient clinical parameters to signal cessation of postpartum magnesium sulfate seizure prophylaxis for the spectrum of pregnancy-related hypertensive disorders.METHODS: This was a prospective study using clinical symptoms (absence of headache, visual changes, epigastric pain) and signs (sustained blood pressure less than 150/100 without need for acute antihypertensive therapy, spontaneous diuresis more than 100 mL per hour for no less than 2 hours) to signal cessation of intravenous magnesium sulfate postpartum in gravidas diagnosed with preeclampsia, eclampsia, and hemolysis, elevated liver enzymes, low platelets syndrome. Laboratory assessments (including proteinuria) were not used as criteria for drug discontinuation.RESULTS: Five hundred three patients were enrolled and classified according to American College of Obstetricians and Gynecologists criteria (mild preeclampsia, severe preeclampsia, chronic hypertension with superimposed preeclampsia, eclampsia, and hemolysis, elevated liver enzymes, low platelets syndrome). Maternal age, gestational age, and hours of magnesium therapy before delivery were not statistically different among groups. There was no significant difference in the duration of postpartum magnesium sulfate therapy among groups with the median duration of therapy 4 hours (range 2-77 hours). No eclamptic seizures occurred after magnesium discontinuation. Thirty-eight patients (7.6%) required reinstitution of magnesium therapy for 24 hours because of exacerbation of blood pressure (sustained blood pressure more than 160/110) associated with headache or visual changes.CONCLUSION: Clinical criteria, when compared with arbitrary protocols, can be used successfully to shorten the duration of postpartum magnesium sulfate administration for seizure prophylaxis in patients with pregnancy-related hypertensive disorders.