If i start pre-preg at 115 pds and gain roughly 20-35 pds, do i risk getting gest diabeties? i'm trying to understand. doc says im a bit underweight.

Depends: Gaining weight does not = gestational diabetes. Go back and ask your doctor why they thought you were at increased risk. They can send you to a nutritionist to help you plan what healthy food choices to make. Age alone due to o age related decreased pancreatic beta cell reserve may contribute but if you have no other risk factors worry less. Keep all appts. Good luck