Cervical length 17 weeks Pregnant

I'm worried about my cervix length. I'm almost 18 weeks and had an ultrasound last week that said I was 2.7 cm?
I have read that a healthy length is atleast 3 cm. However the ultrasound technician and my doctor said mine was okay as long as it was longer than 2.5 cm. I called their office today to double check to make sure it was okay and asked about the length it was at the ultrasound I had 2 weeks before last weeks and she said it was 2.5 at that time. I'm not sure why they didn't tell me it was at 2.5 at 15 weeks if 2.5 is cause for concern. They didn't seem concerned, but I am. Does anyone know anything about cervical length and pregnancy? Is a 2.7 cm cervix healthy at 17 weeks? I have read about many women having a cerclage placed at this length or put on bedrest. My doctor did not seem at all concerned...??? Thank you for your help.

[cristalg13]

my length is 2.7 I'm 16 wks and had a cerclage put in at 13 wks when my length was 3cm if I were you I would see another ob I lost my first baby from oing into labor early I didn't know my cervix was shortening