i did pilates until i was about 23 weeks pg. i told the instructor and i just had to modify some of the positions. but after a while i felt like it was a waste of time because there were more and more things i couldnt do and it felt like i achieved a lot more bu going for a walk! and with the stomach muscles, while the instructor didnt really have me stop doing the ab work, i knew it could be bad to do too much so that is why i stopped in the end.

HTH