Lets all think before we blurt out something hurtful. Mom may be feeling a bit left out, or left behind, stress, whatever you want to call it. If she is expecting soon, hubby will be leaving her behind with TWO children to care for an everybody is paying more attention to the kids, etc. How about some special attention for her. She might like to have some adult conversation just for her once in a while. She perhaps is envious that she doesn't have a "hobby" (they cost $$ and time). Everybody was not brought up with an appreciation for things like sewing, reading, or much of anything that requires personal involvement. Watching TV doesn't require much of anything but electricity and a cable hook-up for the TV set.
I know people who don't see any good in anything that requires effort. They aren't very happy. I do not look forward to talking to them. I also try not to bore them to death with my quilting, embroidery, gardening, or anything else I love to do.
So give MOM a break. We are more mature and know that this too will pass.