Hi paul
koi dont get pregnant , as they reproduced via spawning .
what your seeing , and looking at the pic , that fish does look like she's carrying alot of spawn (eggs ) do you have any males in your pond ??
if you do have some males in there , try and borrow or buy a cheap paddling pool ,and put her and a male in there , and try and get them to spawn , if you cant , and don't have any Male's , cut back on feeding , so she reabsorbs her eggs .
if you not seeing any signs of stress , then i wouldnt be to worried , and mabe buy yourself a male for next year
steve