ABO blood group system alleles in white individuals of the ABO gene that produce one's blood type: The same study also identified 18 rare alleles, which generally have a weaker glycosylation activity. People with weak alleles of A can sometimes express anti-A antibodies, though these are usually not clinically significant as they do not stably interact with the antigen at body temperature. Cis AB is another rare variant, in which A and B genes are transmitted together from a single parent. The distribution of the blood groups A, B, O and AB varies across the world according to the population. There are also variations
Blood type to have anti-D antibodies, the Rh blood type of a fetus can be tested by analysis of fetal DNA in maternal plasma to assess the risk to the fetus of Rh disease. One of the major advances of twentieth century medicine was to prevent this disease by stopping the formation of Anti-D antibodies by D negative mothers with an injectable medication called Rho(D) immune globulin. Antibodies associated with some blood groups can cause severe HDN, others can only cause mild HDN and others are not known to cause HDN. To provide maximum benefit from each blood donation and to extend