In my native India there is a marriage custom like taking a coconut and tying it all around with a red thread. Then on the 5th Friday after marriage the husband and his wife with their individual coconut called 'The coconut for preserving the womb' go and immerse it in a lake. Is there any Ahadith which confirms this? Or is it only a borrowing from the Hindus?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

There is no Hadith proving such a practice.  Indeed, this practice is a polytheist innovation in which some people believe that someone other than Allah can cause harm or bring happiness.

So, the Muslim should avoid such a practice and warn his Muslim brothers against it.

Allah knows best.