At 35.4 weeks can a low grade gum infection harm my baby besides pre term labor?

Yes- brush up! Even a "low grade" infection can be harmful, as your immune system is supressed during pregnancy. So a little infection can turn into a big one. If the bacteria get into your bloodstream, infection can spread, including into the baby. You most likely don't need antibiotics, but you need to big-time improve your oral care, rinse with an antibacterial mouth wash, floss. If worse, let doctor know.