I've tried the mat work before and it was definitely challenging, but once you try the refromer machine----you will soon find out it blows the mat workout out of the water. The pilates reformer machine definitely helps maintain the correct posture and spinal alignment as it's easy to lose proper form on the floor. The original pilates was developed on the reformer back in the early 1900's. The pilates on the mat came many years later for more commercial purposes so people and companies could generate money by selling dvd's videos etc... It's still a good system, but by far---the reformer is much more effective as in showing results quicker.
As far as maintinging my pre pregnancy body---I've managed to do pretty well. I've gained 2 pounds and I'm 26 weeks and the only parts of my body that have increased in size are my boobs and the belly! Other than that---things are still in place! Whew!!! Keeping my fingers crossed!!!
Keep up the work with the pilates---it's definitely well worth it!!
When are you due by the way?? I'm due June 25th....
Good luck!