Collision is a sign of pregnancy (4)
I believe the answer is:
bump
'collision' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for bump that I've seen before include "Evidence of pregnancy - knock (into)" , "Collide - protuberance" , "Lump caused by a blow" , "Collide with force or violence" , "striking" .)