Is this a good cervical length ??

I've been seeing people post about cervical lenght. I've never really thought too much about it but got super curious now since I has badddddd red bleeding during my 15th week. So.. I called my OB office and got my cervical lenght measurement from the receponist, and at 15 weeks it was a 3.9cm ..Is this a good lenght? I'm assuming it's not to be worried about since my OB never said anything ,but I always like to ask my other pregnant mommas on here!