A friend is about 7 months pregnant and was told not to buckle her waist straps on her backpack. When during pregnancy should a woman stop buckling the waist straps?
This will vary by individual - the basic recommendation is that once it becomes uncomfortable you should stop. 6 or 7 months sounds about right.
By that stage though, the recommendation is also to dramatically lighten the pack you carry anyway, as ligaments get much more elastic by that stage of pregnancy and you can do a lot of damage to your joints.