Don't wear your regular slips while pregnant even though they are 'nice and stretchy and feel just fine'.
Because later, when you're not pregnant, that 'nice and stretchy' actually means 'the elastic is shot' and these garments will now ride down somewhere between your hips and your knees. And even though, yes, this means this garment is now showing below the hem of your skirt for all the world to see, that will not be your main concern. Keeping it on your body, however, will be of great concern.
Just so ya know.