But because the child, the fetus is RH positive inside their blood they do have red blood cells that contain antigen D. And when during childbirth some of these red blood cells of the fetus leak into the blood system of the mother, some of these antigen D red blood cells end up in the mother's bloodstream. And now, because the mother is exposed to antigen D for the first time, the immune system will kick in and begin producing antibodies against the antigen D found on those red blood cells that essentially leak into the mother from the fetus. Now this will not actually affect this fetus in any way because this process takes place during and after childbirth. But it will affect any further pregnancies that the mother can actually have, especially if that next child is also RH positive. So once again, during the first pregnancy some of the red blood cells of the fetus that have antigen DRH factor can leak into the mother's blood. Now this leakage of red blood cells that contain antigen D into the mother's bloodstream that is who is RH negative, will cause the immune system of the mother to begin producing antigen D antibodies.