We will construct a pharmacokinetic and pharmacodynamic model of intravenous magnesium sulfate administered antenatally to expectant mothers and exposed fetuses with the aim of optimizing maternal and fetal outcomes while preventing maternal and neonatal overdosing and morbidity associated with current magnesium treatment protocols. Once we have developed a PK/PD model in our own hospital cohort, we will apply this model to a large existing NICHD database to mathematically calculate optimal dosing protocols.