I went to a (non-pregnant) aquarobics class once, many years ago. They held it in the deep end and you were given floats to tie to your ankles and wrists to keep you buoyant so you could just "hang" vertically in the water. But I was ultra-buoyant anyway (too roly-poly) and with the floats on could NOT keep legs under water. So had choice of lying star-shaped on surface of pool, or ditching leg floats and treading water enough to keep me afloat at the same time of doing exercises. I opted for treading water, did the class fine for about 45 mins, then did a few lengths swimming feeling great. Forgot though about weight supporting properties of water, and when i got out I almost sank to the floor as my poor legs were truly done in! Am planning on joining the aqua natal class soon, but very glad to see they do it in shallow end.