The type of blood you have can be very important to understand and it is determined by your genes which you inherit from your parents. The 4 main blood groups are: A, B, AB and O. Each group can either be RhD positive or negative and therefore a total of 8 different groups. It is particularly important in pregnant women who are RhD negative as their may be complications if their baby is RhD positive causing an immune response to baby’s blood.