METHODS
We performed a retrospective cohort study of all deliveries with a
documented QBL from January 1, 2018, to January 1, 2020. Institutional
review board approval was obtained from Boston Medical Center and Boston
University School of Medicine.
At our institution, an interdisciplinary team implemented a postpartum
hemorrhage bundle protocol in 2016 [Appendix S1]. It includes but is
not limited to the following: unit preparation for obstetric hemorrhage,
including simulations, hemorrhage risk assessment on admission
[Appendix S2] and throughout the intrapartum course, quantitative
blood loss (QBL) for all deliveries, and a staged response to the QBL.
Information was gathered from department birth logs that are abstracted
daily from the electronic medical record for all deliveries. This
includes information about maternal demographics, maternal medical and
obstetric history, antenatal course, intrapartum course, anesthesia type
if any, and QBL. Additional information was abstracted by trained chart
abstractors into a standardized chart abstraction form using a secure
database.
We created an OBH-M composite of all cases associated with any of the
following: (i) transfusion of any blood products, (ii) intensive care
unit admission, (iii) clinical, laboratory, or radiologic evidence of
end-organ damage (iv) hysterectomy, (v) operative intervention in the
immediate postpartum period, (vi) uterine artery embolization or (vii)
maternal death. Individual deliveries were categorized into ten equally
sized deciles based on the total QBL. We then compared the proportion of
obstetric-hemorrhage related morbidity within each decile. Among the
deciles with the highest proportions of OBH-M, we stratified deliveries
into seven groups with ascending intervals of 250cc QBL to interrogate a
threshold of QBL associated with an increase in association with a
composite of obstetric hemorrhage-related morbidity (OBH-M). A
significant point in change of risk for OBH-M was established by
sequentially conducting the ranked analysis and stratified QBL-based
analysis.
We then compared the standard definition of OBH (≥1000cc) to the new
definition extrapolated from our stratified analysis (≥1500cc). These
tests included positive predictive value (PPV), negative predictive
value (NPV), sensitivity, specificity, and positive likelihood ratios
(+LR). We utilized a McNemar test to compare sensitivity and specificity
and calculated a post-test probability calculation based on the +LR
values. We also calculated an area under the ROC curve (AUC) for each
definition and compared the AUCs with the DeLong
test.6 An alpha level of 0.05 was used to determine
significance. All analyses were completed using STATA MP, version 17 or
IBM SPSS Statistics 27. 7,8