blood type association with bleeding outcomes at delivery in a large multi-center study

Postpartum hemorrhage is a leading cause of maternal death globally. recent studies have associated type-o group to increased risk of bleeding. we aimed to determine if women with type-o blood are at higher risk of pph. this is a retrospective cohort analysis of a multi-center database included women admitted to labor and delivery from 2015 to 2018. all deliveries resulting in live birth were included. association between type-o and non type-o were examined using chi-square test and fishers exact test. prevalence of postpartum hemorrhage, estimated blood loss, drop in hematocrit and red blood cell transfusion were compared. the matched sample included 40,964 type-o and the same number of no type-o. the overall prevalence of postpartum hemorrhage was 6.4%, and there was no difference in the prevalence of pph among type-o compared to non type-o (6.38% vs. 6.37% respectively; p = 0.96). there was no difference in hematocrit drop and estimated blood loss between type-o and non type-o in all deliveries. however, in cesarean delivery there was a significant difference in blood loss among the two groups. finally, type-o had 1.09-fold increased risk for transfusion compared to non type o (95% ci 0.9–1.34). there is an association between type-o group and risk of bleeding in women undergoing cesarean delivery. more prospective studies, taking into account coagulation profile, platelet count and tissue factors, are needed to draw a conclusion on whether abo system can be considered a heritable risk of postpartum hemorrhage.