How does blood change during pregnancy?
the only thing that changes 'after' pregnancy is whether your blood has produced an anti-Rh or no. Rhesus is the same like antigen but not everyone has it. Rh is antigen D. How do the changes occur? when a mom with Rh- blood marry a dad with Rh+ blood, they will most likely get a baby with Rh+ blood. so, during labour, when the placenta is cut off from the mom, blood mixing happen between the mom and her baby. This will cause the mom blood to be sensitized by the existence of antigen D in the baby blood. When this happens, the mom's blood will produce anti-Rh antibody.
the firstborn will be okay, but the next baby will be affected by the anti-Rh antibody in the mom's blood.