The association between ABO blood group and obstetric hemorrhage.

UNLABELLED: Whether intra- and early post-partum hemorrhage is influenced by ABO blood groups remains unknown. Therefore, we compared women with O to non-O blood groups with regard to maternal post-partum hemorrhage and transfusion need. This retrospective study was conducted in a single tertiary center between 2005 and 2014. For the purpose of the study, parturients were categorized as O and non-O blood groups. Data included all deliveries but excluded patients with missing blood grouping or hemoglobin values, and/or stillbirth. Drop in hemoglobin was defined as hemoglobin concentration at admission for delivery minus lowest hemoglobin concentration post-delivery. Study outcomes were postpartum hemorrhage, hemoglobin drop >2-7 g/dL inclusive, and packed red blood cells transfusion. STATISTICS: descriptive, χ(2) (p < 0.05 significant) and multivariable regression models [odds ratio (OR), 95 % confidence interval (CI), p value]. 125,768 deliveries were included. After multivariable analysis, women with O blood type relative to women with non-O blood type had significantly higher odds of postpartum hemorrhage (OR 1.14; 95 % CI 1.05-1.23, p < 0.001), higher odds of statistically significant hemoglobin decreases of >2, 3, or 4 g/dL (OR 1.07; 95 % CI 1.04-1.11, p < 0.001, OR 1.08; 95 % CI 1.03-1.14, p = 0.002, OR 1.14; 95 % CI 1.05-1.23, p = 0.001; respectively), and higher odds, albeit not statistically significant of 5, 6, or 7 g/dL decreases in hemoglobin (OR 1.13; 95 % CI 1.00-1.29, p = 0.055, OR 1.05; 95 % CI 0.84-1.32, p = 0.66, OR 1.15; 95 % CI 0.79-1.68, p = 0.46; respectively), but no difference in blood products transfusion (OR 1.03; 95 % CI 0.92-1.16, p = 0.58). In conclusion, women with blood type O may be at greater risk of obstetrical hemorrhage.