Update from a doctor: Can cervix shorten and open in 1 day?

So last Friday i went to see my doctor to get answers. The ultrasound showed nothing wrong with my cervix. She performed pelvic exam and everything was fine. But she still told me that she thinks it was due to weak cervix and next time I will get a preventative cerclage, progesterone suppositories and weekly monitoring. I feel relieved but still can’t understand how Incompetent cervix works and how did it shorten and open in just 24 hours! Anyway, i’m happy she offered a cerclage herself and i didn’t have to ask for it

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I suffered loss at 15 weeks due to my waters breaking. When i entered the hospital, my cervix measured 1mm and was open 1.2. I’m very confused because a week before i had two abdominal ultrasounds (the last one was a day before my waters broke) and cervix was 3,9 and closed. Still, the doctor at the hospital told me without any examination that it was probably IC and that i needed to get examined (which i do next week). But i don’t understand, does this happen with IC? Can cervix be fine one day and then completely shorten and open the next day? Could it be that my waters broke first and then cervix shortened?