Why would i be given rh factor?

Protect next child: If you are rh negative & your newborn rh positive, then you will develop antibodies against rh positive blood. If your next child is also rh positive these antibodies may cross the placenta causing a serious problem, hemolytic anemia. In that case your newborn will be very ill & may require many blood transfusions. Rh factor helps prevent you from developing these dangerous antibodies.

Rh factor antibodies: Rh is a red blood cell surface marker. When a mother lacking this marker (rh -) has a pregnancy with an rh+ infant, she may make antibodies to the babies blood causing the baby to be anemic (low red blood count). This may be very dangerous. To prevent this the mother can be given an injection of rh antibodies to prevent her from making the antibodies that might attack her baby's blood.