Rhesus factor and anti-D
The blood group factor RhD (aka Rhesus factor D) is one of many known blood group factors. RhD, however, is highly immunogenic, which means that carriers of the RhD-negative factor often form antibodies against RhD when they come into contact with red blood cells (erythrocytes) that have the RhD blood group factor.
During pregnancy and childbirth, small amounts of erythrocytes in the fetus can enter the maternal bloodstream. If the fetus has the blood group factor RhD-positive and the mother is RhD-negative, the mother may be “sensitized” or “immunized”. The antibodies formed against Rhesus factor D are called “anti-D”.