The four main blood group types are A, B, AB and O. Determined by the genes in oneself, an individual's blood group is inherited from the parents. Additionally, a protein known as the Rh Factor, is either present as Rh-positive (+) or absent as Rh-negative (-), therefore creating eight common blood group types.  

What is the Rh Incompatibility? 
The Rh or 'Rhesus' factor, an inherited protein, is found on the surface of the cell membranes of red blood cells. If your blood contains the protein, you are Rh-positive, if it does not, you are Rh-negative. However, having the Rh blood type is a normal condition and does not imply that one has a disease or that it could generally alter your health.