The moms in my prenatal class really seem to like doing abs with a stability ball. I put one ball in between two exercisers... or else they put the ball in between themselves & the wall. We do belly breathing (navel to the spine, as tight as possible) while pressing the small of their backs into the ball, regular presses into the ball, pulses, 2 counts in/2 counts out ("in and in, release, release"). I stress that my moms need to really concentrate on making each muscle contraction tight in order to work the muscle well. We do obliques in the form of tail wags on hands and knees). I've also recently begun to do some stability exercises with my moms. We sit on two 8 inch steps, and do very slow marches, alternating feet... you have to engage your abs in order to do this. Finally, we do a lot of our upper body resistance exercises with dynabands while sitting on stability balls. Again, in order to balance on the balls, you have to use your abs for stability.
My boss is 34 weeks along, and she is still teaching regular classes -- like Cathe, she also does her abs on an incline.
susan