If you are trying to export NURBS geometry and trying to maintain it as such in Rhino, then you do need to export as IGES. However, if you are trying to export a Mesh or Polygons you should use FBX, which is the standard format for polygon objects that have dimensions and are to be used in CAD programs.
Otherwise, you will just get curves when you export a polygon, as IGES
translates the polygon edges to curves or splines.
here is the link to the plug-in, if you don't already have it