An Antibody with antigen occuring in the red blood cells.
Complications and Defects
RH Factor causes defects and complications of your baby if you and your husband are opposite RH factor blood types. There is no cause and there is no way to prevent which blood type you have.
When you first realize you are pregnant, you have to go and get a normal blood test, and that's all you need to figure out which blood type you are.
The only treatment you can have is to go to your doctor and get a shot of RH immunoglobulin while you are pregnant.
How to prevent
There is no way to prevent it, but you can treat the mother during pregnancy, and that with help the baby.