Who are the people that need to take Rh immunoglobulin?

Obstetrics. If mom is rh blood negative and baby is rh-positive, then mom needs the rh-immunoglobulin to prevent future serious problems with other births.
Rh sensitization. Rh sensitization can only occur if an rh negative person is exposed to rh positive blood. This can happen with blood transfusions or from rh positive fetal blood spill-over into the mother's blood stream during delivery. Once formed, these antibodies can harm future pregnancies. If the baby's dad is rh positive, rh negative mom's should get an injection of rh antibody to stop her production.