Why Do Pregnant Women Attach Safety-Pin(s) To Their Clothes?

Oftentimes when I come across pregnant women ,I can't help but noticed a pin attached to their outfit.

This actually have got me wondering why our pregnant women always attached safety pin(s) to their clothes/wears.

From my observation,It seems to be a common practice among the yorubas,but i don't know if this is also applicable to other culture/tribes in Nigeria.

From my findings during an interactive section with an elderly man who revealed that the "Safety pin" is usually attached to pregnant women's clothes/wears so as to protect the foetus from evil spirit/demons who according to him operates mostly in the afternoon and night!