Incompetent cervix causes

For all the mamas with an incompetent cervix and no previous risk factors: I understand that, according to current research, there is no clear explanation for why this happens to some women. Apparently some of us are born with weak cervix. However, based on my experience, I strongly believe that my cervix opened due to severe stress I was under at work. I’m curious to hear if you have any theories about what might have caused it for you.