Im 53, currently 150lbs at 5 months pregnant (130 lbs pre-preg weight, size 6-8, wide hips/butt) and I ordered a medium and it fits as expected. The slip provides good coverage - but FULL coverage - The straps are wide and the front comes up really high on the chest so it limits what you can wear this under. I prefer a low cut slip with spaghetti straps but its impossible to find in maternity sizes. I haven't had any issues with the slip riding up and although its snug (its supposed to be) its pretty comfortable and I don't feel any unwanted pressure on my belly.