why do men grow a beard when wife is pregnant?

I have been encountering with some of my friends, colleagues and relatives here and there who are growing beard heavily and I asked them why are they growing the beard and they respond -

"My wife is pregnant?!"

I could not find a valid reason. I have also heard from them that the reason is religious. I could not find any religious reason in the internet - nobody has written it.

However - "a Caucasian male has written in internet that - he is growing a beard so that they will not have any relationship in bed and they could avoid an immediate pregnancy right after their pregnancy? Good reason."

But, I am looking for a valid reason still - why do men grow a beard when his wife is pregnant? Actually, they shave off as soon the baby is delivered.

Let me know if you find the reason!