Calculating probability of requiring allogeneic blood transfusion using three preoperative risk factors on cesarean section for placenta previa

To construct a model to calculating probability of requiring allogeneic blood transfusion on cesarean section (CS) for placenta previa (PP). A retrospective cohort study involving all 205 patients with PP who underwent CS in our institute. We determined the relationship between allogeneic blood transfusion and nine preoperative factors: (1) maternal age, (2) parity, (3) uterine myoma, (4) previous CS, (5) the placenta covering the previous CS scar (referred to as "scar covering"), (6) degree of previa, (7) ultrasound finding of lacunae, (8) preoperative anemia, and (9) preparation of autologous blood. Independent risk factors of allogeneic blood transfusion were identified by multivariate logistic regression analysis. These significant factors were included in the final model, and, the probability of allogeneic blood transfusion was calculated. Independent risk factors of allogeneic blood transfusion were scar covering, previous CS without scar covering, and lacunae. These three factors were used to create a predictive model. The model revealed that patients with scar covering and lacunae had the highest probability (0.73), while those with no risk factors had the lowest probability (0.02). This simple model may be useful to calculate probability of requiring allogeneic blood transfusion on CS for placenta previa.