Calcium Chloride for Prevention of Uterine Atony During Cesarean

Inclusion Criteria: Pregnant female subjects at Lucile Packard Children's hospital / Stanford hospital undergoing Cesarean will be screened for inclusion in the study based upon presence of at least 2 risk factors for uterine atony/ postpartum hemorrhage. The risk factors include the following: * intrapartum Cesarean delivery * failed operative vaginal delivery with forceps or vacuum * magnesium infusion * chorioamnionitis * multiple gestation * polyhydramnios * preterm delivery \<37 weeks * prior history of postpartum hemorrhage * labor induction or augmentation with oxytocin * advanced maternal age * obesity with body mass index \>40 Exclusion Criteria: * a degree of case urgency to which taking time to consent for the study could compromise patient care, determined by anesthesiologist or obstetrician * patient age \<18 years or \>50 years * renal dysfunction with serum Creatinine \> 1.0 * abnormal cardiac function or history of arrhythmia * patient taking digoxin * patient currently taking a calcium channel blocker for a cardiovascular indication