Maternal Transfusion May Overestimate Severe Maternal Morbidity When Used As An Indicator

Although blood transfusion (TF) has been classified as an indicator of severe maternal morbidity (SMM), some patients receive blood without experiencing other morbid events possibly inflating rates of SMM. As many scientific bodies consider ≥ 4 units RBC to be significant for SMM, we sought to compare rates of SMM by this cutoff. This retrospective analysis included all women who delivered in a four-hospital system from January 2016 through January 2020. Demographic and clinical data were extracted using an automated query from the hospital system's electronic data warehouse, which aggregates data from the EHR, billing system, and other sources. Our primary analysis was to examine the rate of non-transfusion related SMM indicators (ntSMM) stratified by the number of units of RBCs (uRBC) transfused. ntSMM were identified using billing codes and receipt of blood TF was identified based on electronic orders. We then examined rates of specific ntSMM by units transfused. The cohort included 60,034 deliveries of which 1,452 (2%) received at least 1uRBC and of these 254 (17.5%) received ≥4uRBC. Patients who received ≥4uRBC tended to be older and have lower hematocrits prior to delivery with similar race, ethnicity and payer status. The average number of ntSMM increased when ≥ 4uRBC were transfused with 98% having at least one ntSMM (figure 1). Of those who received ≥ 4uRBC, the most prevalent ntSMM were hysterectomy (22.8%), disseminated intravascular coagulation (16.9%), sepsis (14.6%), shock (13.8%), acute kidney injury (11.8%) and acute respiratory distress syndrome (4.3%) (table 1). Among those who received <4uRBC, all individual ntSMM indicators were detected at rates ≤ 3%. An overwhelming majority of patients transfused ≥4uRBC have an associated ntSMM, making its use as a trigger for case review appropriate but use as a separate indicator of SMM unnecessary. Also, as a minority of patients with <4uRBC transfused have an associated ntSMM, the use of transfusion as an indicator may overestimate morbidity.View Large Image Figure ViewerDownload Hi-res image Download (PPT)