Possible cerclage or not?

I have been having cervical length scans, due to a previous loss at 22 weeks. The first scan shown my cervix at 47mm - great! 2 weeks later, it was measuring 30mm, with unknown fluid on it too. I was started on progesterone and given an appointment 1 week later. 1 week later, my cervix measured at 34mm, still with unknown fluid. I have been tested for infection yet again, and given precautionary antibiotics. The consultant said that a cerclage is the most likely option and I need to decide whether it is done electively or as an emergency. I was under the impression that a cerclage was only for a shortening, cervix- which of course mine might but at the minute doesn't seem to be. Has anyone had anything similar happen? Anyone had fluid on their cervix, and are happy to share their experience? Next week, I want to go to the consultant armed with questions and perhaps a better understanding of what I might be dealing with before I commit to a cerclage. Thanks.