Increased risk of hemorrhage in patients with mild thrombocytopenia at delivery admission.

Objective: Maternal hemorrhage is a major contributor to pregnancy morbidity and mortality worldwide. Identifying risk factors for hemorrhage is critical to optimizing patient safety and preventing patient morbidity. Prior studies examining the potential association between mild thrombocytopenia and the risk of postpartum hemorrhage have had inconsistent findings. In this study, we seek to investigate whether mild thrombocytopenia increases the risk of clinically significant obstetrical hemorrhage in a large, modern cohort. Methods: This is a retrospective cohort study of patients delivering ≥ 24 weeks singleton gestations within a single hospital system between 2013 and 2023. Data were extracted from the hospital electronic medical record (EMR) data warehouse using standardized definitions and diagnosis codes. Patients were categorized as having normal platelets (≥ 150 × 1000/µL) or mild thrombocytopenia (100-149 × 1000/µL) at delivery admission. The primary outcome was a bleeding composite inclusive of estimated blood loss at delivery ≥1000 mL, International Classification of Diseases (ICD) diagnosis of postpartum hemorrhage, or receipt of a red blood cell transfusion. Secondary outcomes included (1) additional uterotonic use after delivery other than synthetic oxytocin; (2) tranexamic acid use; (3) need for a hemorrhage procedure; (4) intensive care unit admission. Multivariate logistic regression was performed for the two statistically significant outcomes adjusting for potential confounders. Results: Among 85,047 eligible subjects, 7194 (8.5%) had mild thrombocytopenia noted upon admission for delivery, while 77,853 (91.5%) had a normal platelet count. Patients with mild thrombocytopenia were more likely to be advanced maternal age, multiparous, have preeclampsia with severe features, have a neonate > 4000 g, and have an admission hemoglobin < 11 g/dL. Mild thrombocytopenia was associated with a higher risk of the bleeding composite (7.6% vs. 6.7%, aOR 1.22, 95% CI 1.11-1.34) and uterotonic use (13.4% vs. 11.7%, aOR 1.17, 95% CI 1.09-1.26) compared to normal platelet count group. Conclusion: Patients with mild thrombocytopenia at the time of delivery hospitalization had increased odds of clinically significant postpartum bleeding. This patient population is not traditionally considered to be at increased risk of clinically significant hemorrhage; however, this variable should be considered in risk assessment tools to better identify patients at risk for hemorrhage.