Investigation of Intrapartum Parenteral Magnesium Sulfate as an Independent Risk Factor for Postpartum Hemorrhage Using Quantitative Blood Loss Assessment

BACKGROUND: Magnesium sulfate is used for seizure prophylaxis in preeclampsia and for fetal neuroprotection when delivery is anticipated before 32 weeks of gestation. Existing risk assessment tools for postpartum hemorrhage often identify the use of magnesium sulfate as an intrapartum risk factor. Previous studies examining the association between the use of magnesium sulfate and postpartum hemorrhage have relied largely on qualitative estimates of blood loss rather than quantitative estimates of blood loss. OBJECTIVE: This study aimed to determine whether intrapartum administration of magnesium sulfate is associated with an increased risk of postpartum hemorrhage using a quantitative blood loss assessment via the use of graduated drapes and weight differences in surgical supplies. STUDY DESIGN: This case-control study was conducted to test the hypothesis that intrapartum parenteral administration of magnesium sulfate is not independently associated with postpartum hemorrhage. All deliveries at our tertiary-level academic medical center between July 2017 and June 2018 were reviewed. Of note, 2 categories of postpartum hemorrhage were defined: the traditional definition (>500 mL for vaginal delivery and >1000 mL for cesarean delivery) and the contemporary definition (>1000 mL regardless of delivery mode). Statistical analyses using the chi-square test, Fisher exact test, t test, or Wilcoxon rank-sum test were performed to compare the patients who did and did not receive magnesium sulfate concerning the rates of postpartum hemorrhage, pre- and postdelivery hemoglobin level, and rates of blood transfusion. RESULTS: A total of 1318 deliveries were included, with postpartum hemorrhage rates of 12.2% (traditional definition) and 6.2% (contemporary definition). Multivariate logistic regression did not find the use of magnesium sulfate as an independent risk factor by either definition (odds ratio, 1.44 [95% confidence interval, 0.87–2.38] and 1.34 [95% confidence interval, 0.71–2.54]). The only significant independent risk factor was cesarean delivery, by both definitions (odds ratio, 2.71 [95% confidence interval, 1.85–3.98] and 19.34 [95% confidence interval, 8.55–43.72]). CONCLUSION: In our study population, intrapartum administration of magnesium sulfate was not found to be an independent risk factor for postpartum hemorrhage. Cesarean delivery was determined as an independent risk factor, consistent with previous reports.