The trial will test the equivalence of a repeat bolus protocol of magnesium sulfate administered by the Springfusor® controlled pump to a continuous intravenous regimen. The goal of this pharmacokinetic study is to assess the pharmacological equivalence of the serum magnesium sulfate concentrations obtained in the treatment of severe preeclampsia with the continuous intravenous and Springfusor repeat bolus regimens. The study will also document the clinical outcomes, efficacy and acceptability of each treatment for patients and staff.

Inclusion Criteria:

Exhibit systolic blood pressure > 160mm Hg OR a diastolic pressure > 110 mm Hg (at two times over 30 minutes) (A single higher pressure could be accepted if the clinical team felt that magnesium sulfate therapy should be initiated without waiting 30 minutes).

Exhibit proteinuria > 1+; Have not given birth, or be <24h postpartum Be assessed by enrolling physician to benefit from magnesium sulfate therapy Agree to comply with study procedures Be > 18 years of age Give informed consent for study participation

Exclusion Criteria:

Eclamptic or seizing at the time of enrollment Received magnesium sulfate therapy 24h prior to study enrollment Known serum creatinine >1.2 mg/dL. (Subject may be enrolled prior to knowledge of serum creatinine but would be withdrawn if >1.2 mg/dL in order to have a proper dose adjustment.