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what is Rh+,and Rh factor?how it causes erythryoblastosis foetiles?
Rh  blood types were discovered in 1940 by Karl Landsteiner and Alexander Wiener.
The Rh system was named after rhesus monkeys, since they were initially used in the research to make the antiserum for typing blood samples.  If the antiserum agglutinates your red cells, you are Rh+, if it doesn't, you are Rh-.
Rh type mother-fetus incompatibility occurs only when an Rh+ man fathers a child with an Rh- mother.  Since an Rh+ father can have either a DD or Dd genotype, there are 2 mating combinations possible with differing risks. Regardless of the father's genotype, if he is Rh+ and the mother is Rh-, doctors assume that there will be an incompatibility problem and act accordingly.
The first time an Rh- woman becomes pregnant, there usually are not incompatibility difficulties for her Rh+ foetus.  However, the second and subsequent births are likely to have life-threatening problems for Rh+ foetuses.  The risk increases with each birth.  The placenta is an organ that connects the foetus to the wall of the uterus via an umbilical cord.  Nutrients and the mother's antibodies regularly transfer across the placental boundary into the foetus, but her red blood cells usually do not (except in the case of an accidental rupture).  Normally, anti-Rh+ antibodies do not exist in the first-time mother unless she has previously come in contact with Rh+ blood.  Therefore, her antibodies are not likely to agglutinate the red blood cells of her Rh+ fetus.  Placental ruptures do occur normally at birth so that some foetal blood gets into the mother's system, stimulating the development of antibodies to Rh+ blood antigens.  As little as one drop of foetal blood  stimulates the production of large amounts of antibodies.  When the next pregnancy occurs, a transfer of antibodies from the mother's system once again takes place across the placental boundary into the foetus.  The anti-Rh+ antibodies that she now produces react with the fotal blood, causing many of its red cells to burst or agglutinate.  As a result, the newborn baby may have a life-threatening anemia because of a lack of oxygen in the blood.  The baby also usually is jaundiced, fevered, quite swollen, and has an enlarged liver and spleen.  This condition is called erythroblastosis fetalis.


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