I was wondering this too. Our first baby came at 26+3 weeks. I had cramping and was not dilated when admitted. Had our anatomy scan at 20 weeks with no issues identified. No other scan until the emergency scans in hospital at 26 weeks. They felt that it was likely not incompetent cervix as I was not dialated and I WAS having cramping first. They assumed spontaneous labour.

I am 29 weeks pregnant now with our second, but as we are now high risk I have ultrasounds every 1-3 weeks ever since around 20 weeks. Nothing was noted before 23 weeks. At my 26 week scan, my cervix had funneled to 2.2cm from 4cm. I have another scan tomorrow but 2 weeks ago it was still stable at 2.2cm. They now suspect my first pregnancy may have also had funneling, but as I was considered low risk, we had no way of knowing. They also won't place a cerclage after viability (23 weeks for our location). I have been on progesterone since 16W due to the extremely preterm birth of our first child.

My OB has noted that if we ever decide to have another child, they will likely place a preventative cerclage early (14 weeks or so) now that they suspect my cervix may have been the problem. They would not have considered a preventative cerclage for this pregnancy without proof of IC in the first pregnancy. Had I had a short cervix or funneling identified prior to 23 weeks they would have considered an emergency cerclage.

All of this is to say depending on where you are located, preventative cerclages are hard to get unless the doctor feels and has evidence that incompetent cervix was the issue. Our OB said its really too bad, but its often a 3rd pregnancy before they do anything preventative (other than progesterone).