MS-2988

A 35-year-old obese nulliparous woman has given birth to a live singleton and the placenta, but is experiencing excessive bleeding. The registrar estimates that she has lost around 600 ml of blood. Despite receiving both crystalloid and colloid fluids, she remains haemodynamically unstable. As crossmatched blood is not yet available and her blood group is unknown, what blood group should be given to prevent a transfusion mismatch?