She's due in May. Would she be showing anything yet? Are some horses like women and just don't ever show much. I remember when she was pregnant with Dot, she didn't show much, but that was her first, and she was in tip top shape. I thought this time she'd show more, sooner.
Becky
Right now the biggest change will be in her behavior - some mares don't balloon out until late in pregnancy. She should be getting lazy and laid back by now though, sleeping in the sun if you have any.
Don't worry until after the vet check, she's probably fine. At this point, he shouldn't be able to miss a foal :) (I have one that sure looks pregnant but the vet said she was open a few months ago.)