Pcos with insulin resistance. 26 wks pregnant. fasting blood sugar each month about 68. failed one hour glucose 146. do i have gd or is fail due to ir?

Not sure: you can tell. As you suggest, PCOS is associated with insulin resistance, a condition which existed before you were pregnant. In this setting, hyperglycemia is induced more easily, although your fasting blood sugars are reassuring. If you were in my office, I would probably say, "Not sure you would have had GD if you did not have preceding PCOS, but abnormal 1 hr GTT puts you in GD risk category."