The blood group may be included on identification tags or on tattoos worn by military personnel, in case they should need an emergency blood transfusion. Frontline German Waffen-SS had blood group tattoos during World War II. Rare blood types can cause supply problems for blood banks and hospitals. For example, Duffy-negative blood occurs much more frequently in people of African origin, and the rarity of this blood type in the rest of the population can result in a shortage of Duffy-negative blood for these patients. Similarly, for RhD negative people there is a risk associated with travelling to parts of the world where supplies of RhD negative blood are rare, particularly East Asia, where blood services may endeavor to encourage Westerners to donate blood. Hemolytic disease of the newborn (HDN)
A pregnant woman may carry a fetus with a blood type which is different from her own. Typically, this is an issue if a Rh- mother has a child with a Rh+ father, and the fetus ends up being Rh+ like the father. In those cases, the mother can make IgG blood group antibodies. This can happen if some of the fetus blood cells pass into the mothers blood circulation (e.g. a small fetomaternal hemorrhage at the time of childbirth or obstetric intervention), or sometimes after a therapeutic blood transfusion. This can cause Rh disease or other forms of hemolytic disease of the newborn (HDN) in the current pregnancy and/or subsequent pregnancies. Sometimes this is lethal for the fetus; in these cases it is called hydrops fetalis.
To resolve the confusion, the American Association of Immunologists, the Society of American Bacteriologists, and the Association of Pathologists and Bacteriologists made a joint recommendation in 1921 that the Jansky classification be adopted based on priority. But it was not followed particularly where Mosss system had been used.In 1927, Landsteiner, who had moved to the Rockefeller Institute for Medical Research in New York, and as a member of a committee of the National Research Council concerned with blood grouping suggested to substitute Janskýs and Mosss systems with the letters O, A, B, and AB. There was another confusion on the use of O which was introduced by Polish physicians Ludwik Hirszfeld and German physician Emil von Dungern in 1910. It was never clear whether it was meant for the figure 0, German null for zero or the upper case letter O for ohne, meaning without; Landsteiner chose the latter. In 1928 the Permanent Commission on Biological Standardization adopted Landsteiners proposal and stated:The Commission learns with satisfaction that, on the initiative of the Health Organization of the League of Nations, the nomenclature proposed by von Dungern and Hirszfeld for the classification of blood groups has been generally accepted, and recommends that this nomenclature shall be adopted for international use as follows: 0 A B AB.