Antibodies to the red cell Rhesus D (RhD) antigen can be produced during pregnancy in a RhD-negative mother carrying a RhD-positive fetus, in particular following feto-maternal haemorrhage at birth or following any procedure that may cause feto-maternal haemorrhage. While the first baby is usually not harmed, these antibodies may cause haemolytic disease of the fetus/newborn (HDFN) in subsequent RhD-positive babies. RhD incompatibility is a major cause of HDFN.
To reduce the risk of HDFN, anti-D is given to RhD-negative mothers at 28 or 30 weeks of pregnancy and within 72 hours of potential maternal exposure to fetal red cells. Anit-D is currently available in both intramuscular (IM) and intravenous (IV) preparations.