The article I pasted below explains it pretty clear. My sister is Rh negative and had to get the Rhogam shots when she was pg with all 3 of her boys. All are just fine :)
During pregnancy, Rh-negative is the only one of these blood groups that can cause a problem. It turns out that an Rh-negative mother can make antibodies (part of her immune system's response to invaders) against Rh-positive blood cells, even against those of her own baby. This is called Rh sensitization. These antibodies have the potential to cross the placenta and attack the fetus' red blood cells, which in turn can cause low blood count (anemia), congestive heart failure, and even fetal death. This is called hemolytic disease. Fortunately, Rh sensitization is preventable with a medicine called Rh immunoglobulin (RhIg, or Rhogamâ„¢.) Since the development of RhIg, in 1968, we have seen fewer and fewer mothers who are Rh sensitized.
I forgot to add, blood type shouldn't affect fertility at all. The problem it causes is in carrying.