Cervix slightly open at 18 weeks

Hello.  I went for my 18 weeks anatomy ultrasound a few days ago.  The technicians noticed that my cervix seemed slightly open and sent me to another place to get another ultrasound done.  They confirmed that my cervix is slightly opened (I don't know how much), but that it was 3.3 cm long. The doctor did a pelvic exam and said that my cervix felt firm (like a nose) and since it was long that no immediate treatment was necessary.  He thought that what might look like openness on the ultrasound might be fluid in my cervix, rather than open space, but had no real evidence to support that theory.  I have to go back again in 2 weeks for another ultrasound to check cervical length, and at that time I'll be 20 weeks.  So here are the questions...1) If my cervix remains the same length and amount open, will that mean I'm in less danger of going into labor or delivering preterm?  2) If my cervix shortens below 2.5 cm, can a cerclage still be done at 20 weeks?  3) Has anyone ever heard of fluid in the cervix showing up on the ultrasound and looking like open space?? I'm kind of freaking out because the doctor said his "gut" told him I'd be fine.. but I'm not sure I feel comfortable relying on someones gut!

[AnnieBrooke]

I assume you mean it has a funnel?  In other words, it is partly open from the inside, not from the outside?  I went through the entire second half of my pregnancy with a funnel, which my doctor was unconcerned about -- she said "As funnels go, it's a pretty wimpy funnel."  If memory serves, my remaining cervix that was shut was 3.5 cm.  It never opened any further until I was ready to deliver.  They would have gotten interested if it had dropped to below 3.  When does your doctor plan to look at it again, and did he say anything about cerclage?  

[Christina0502]

I don't know, they didn't use the word funnel.  I'm not sure where it's open, all I know is when he did a pelvic exam he said it felt firm from that end at least.  I go again on Nov 17th.. we discussed the cerclage, but he said for right now there is no evidence that would support using one.  I just don't want it to be too late when I go on the 17th if things have thinned below 3cm.