The helix shapes are created using a screw modifier. Everything looks good in the 3d view (with render preview on)
but when I actually hit render.. the helix shape is not rounded, and has a funny hard edge look.
If you're using a subdivision surface modifier for the helix, keep in mind the modifier has different levels for previews and renders as seen here:
this may explain why your helix has a funny look when you render it
I guess the problem is the Render step of your modifier. Also, you have to check if all of your used modifiers have the same resolution in the preview and render mode.