There is a culture of making pregnancy women wear iron Bangles. is there any religious angle to this? Should we wear the bangle just because our elders say it or should we avoid? Is believing in such traditions that bangles help against feeling afraid shirk?

These are traditions, which has no relation to religion. It is up to you to do it or not to do it.
If you believe that these things have effect, then it is a type of shirk.