Interrupted versus continuous magnesium sulfate and blood loss at cesarean delivery.

Objective: Magnesium sulfate is standard of care for prevention of eclampsia in women with preeclampsia with severe features. The American College of Obstetrics and Gynecology endorses its use throughout labor, delivery and the immediate postpartum period. Some providers pause magnesium sulfate infusion preoperatively due to concern for increased risk of uterine atony and postpartum hemorrhage. Using a non-inferiority analysis, we investigated the effect of interrupted versus continuous infusion of magnesium sulfate on postpartum hemorrhage in women with preeclampsia with severe features undergoing cesarean delivery.
Study Design: Retrospective non-inferiority cohort study of women with preeclampsia with severe features treated with magnesium sulfate undergoing cesarean delivery with singleton pregnancies at tertiary care hospital from 2013 to 2018. The primary outcome was postpartum hemorrhage. Secondary outcomes included estimated blood loss, change in hematocrit and a composite of postpartum hemorrhage severity, including transfusion of blood products, use of more than one uterotonic and additional surgical interventions.
Results: Of 249 women, magnesium sulfate infusion was interrupted in 171 (69%) and continued in 78 (31%). Women with interrupted magnesium sulfate infusion were more likely to be Caucasian (73% vs 67%, p  = .024), have chronic hypertension (23% vs 1%, p  < .001), labor prior to cesarean delivery (84% vs 55%, p  < .001), undergo primary cesarean delivery (86% vs 67%, p  = .005), and experience shorter surgical time (50 vs 55 min, p  = .026). The rate of postpartum hemorrhage for those receiving interrupted magnesium sulfate infusion (9.9%) and continuous magnesium sulfate infusion (10.2%) was similar, falling within the non-inferiority margin (absolute difference 0.3%, 95% CI -7.8 to 8.4%, p  = .88). There were no significant differences in the secondary outcomes.
Conclusion: Interrupted magnesium sulfate infusion is non-inferior to continued magnesium sulfate infusion for rates of postpartum hemorrhage in women with preeclampsia with severe features undergoing cesarean delivery.