It seems from your test results that the antibodies (IgG) against the Rubella virus didn’t damage the foetus - the virus itself did that. Antibodies in fact, protect the body. Antibodies against viral infections are usually detected a few weeks after an infection. You probably had a case of Rubella during the first pregnancy which generated the creation of IgG-antibodies. Antibodies persist in your body’s blood for a long time ...even after infection is cured. During the second pregnancy, the presence of IgG-antibodies does not indicate a rubella infection but immunity against the infection. It seems that you don’t need any treatment because you became resistant to the rubella-virus during your first exposure to the infection.