RHD and prion disease: However, in the UK, about 40% of RhD− women (around 40 000 per year) carry an RhD− fetus and thus receive anti-D unnecessarily.2 Anti-D is produced from pooled plasma from large numbers of RhD− donors who have been transfused with RhD+ red cells to stimulate the production of RhD antibodies3 and thus carries a very small risk of transmission of human blood-borne viral or prion diseases.4