Hi Bex - sorry for late reply hun, been super busy today
I had a dilated cervix and bulging membranes in my second pregnancy discovered at 23wks, had an emergency stitch placed, and made it to 24. I had a doctor willing to place a stitch at that late stage when many others won't attempt it - thankfully it bought us an extra week and my daughter is now a healthy 6yr old

I also had a stitch placed in my most recent pregnancy (twins) at 12wks and made it to 38wks.
Ok - your cervix is currently dilated, but if I understand you correctly it is dilated at the bottom and not the top? Towards the end of pregnancy, a cervix begins to soften, thin out and slowly dilate from the top down (funneling). If a cervix is incompetent then this starts to happen (without contractions) anywhere from 15 to 24wks. It literally "gives way" under the growing weight of the baby.
I don't think that this is what's happening with youl because your cervix is open at the bottom, much like it is after a woman has previously given birth. Your doc is probably uncertain himself and is operating a "wait and see" approach on the basis that you haven't gone on to dilate further, and the pregnancy is still healthy.
I personally would push a bit more towards having a stitch just in case, but obviously you can't insist on this, and as your doc already mentioned this can cause more problems than not if your particular issue is not incompetent cervix.
A stitch is placed about half way up the cervix and pulled tight like a purse string, so it would be possible to place one above the opened section, and it would certainly prevent it opening further (top down). I think your doc was referring to the possibility of infection in placing a stitch in an already open cervix, when in fact it may be better to leave well alone, and that is always a risk once your cervix has opened even slightly.
What is important is that you have a good length of closed cervix leading up to your uterus, since this is what prevents infection from travelling north - as it stands, you do and the opening is at the bottom - not currently a risk.
I am not an expert hun, so don't want to push you down a road that isn't right for you, but it might be worth asking a few more questions if nothing else to put your mind at rest. I would say that at the moment there is nothing immediately to worry about, but if you do feel any increased vaginal pressure/bulging sensations, and/or you get any extra discharge/bleeding, then to go immediately to get checked out again.
Are they scanning you again soon? Incidentally, did he do an internal scan?
Hope this message isn't too garbled and makes some sense? I am exhausted and aware that I'm not putting "pen to paper" very well
Try to relax my sweet - it is frightening, but at the moment things are still ok xxx