Not really, you won't notice much till the last few months. Her belly of course will get big, she will start to bag up (get milk). I had a mare that was maybe, maybe not pregnant and we didn't really know till about a week or so before she gave birth. I do continue to ride the last 2 pregger girls I had till the last month before they foaled. I rode Vida the day before for about 10 min. bareback in the round pen.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France