This suit is great for casual swimming, I love the supportive bra and style. I did try lap swimming in it (I swim about a mile several times a week) and it chafed on the halter part so I wouldn''t recommend this for exercise. Probably fine for aqua aerobics.
I wasn''t sure about size, I''m a size 4/small in regular clothes pre pregnancy, so I got the 6 and it fits just fine. I''m 6 1/2 months and there is room to grow.