Are there things I can do myself to treat macrosomia?

Pre or postnatal? Prenatally, you can get your glucose under control. After birth, try to rule out glucose issues as well, physician will try to rule out cong syndromes including beckwith- wiedemans.
Control diabetes. I f you referring to treating macrosomia of fetus while you are pregnant, the best tool is controlling your blood sugar/glucose levels and ensuring if you have diabetes that it is treated correctly with diet and medications.