I got this over the one piece because it overall is much easier to put on and take off! I got the size M, and pre pregnancy I was a size 8 in women''s at about 150 lbs and 5ft 8in. Now I am 27 weeks pregnant, and have gained about 20 lbs and have been using this about 2 times a week for lap swimming for the past 5 weeks. The top was too big for me, pre-pregnancy I was a 36 B bra size and would say I''m a full C cup now and the top is still too big. I ended up tailoring it to fit my smaller chest, and I like the tighter fit for lap swimming anyway. It fits great over my bump, snug without being tight and the drawstring helps a lot, the top never comes up even when I do filp turns. I like that there is still room to grow, which is good because I''ve still got 13 weeks or so. Overall very good quality, not see through at all and I like that I can use this for recreational outings too and it doesn''t look like a lap suit.