text: It would depend on the sense in which you were using it. It's not a common expression in English.  If you were describing the way a garment looked, say, a long white dress, broken at the waist by a pink sash.  If you were speaking of a  vessel, such as a vase, which was damaged at the narrowest point, it could be broken at the waist. It would not be used either way to describe  an anatomical break, I don't think. \nThe only way you could use "by the waist " would be to explain a shape altered by the waist.