A key risk of blood transfusion in obstetrics is a Hemolytic transfusion reaction, which occurs when the recipient's immune system attacks transfused red blood cells. This reaction can lead to acute hemolysis, intravascular coagulation, renal failure, and even death. Obstetric patients are particularly vulnerable due to potential alloimmunization and sensitization from previous pregnancies or transfusions. Prompt recognition and management are critical to prevent severe complications. Other options like hypertension, hyperglycemia, or constipation are not directly linked to transfusion risks in this setting.

Reference: Williams Obstetrics, Cunningham FG, 25th Edition.