Shortening cervix 17 weeks

I'm 37. Lost our first last year due to PPROM along with a fibroid complication. I had the fibroid removed.  Got pregnant in Feb.  Drs watching cervix as a precaution but thought my last loss was solely due to the fibroid.  Started progesterone shots at 16 weeks with cervix length of 3.something.  Then at 17 weeks it went down to 2.7. Dr added vaginal progesterone suppositories.  I go back Wednesday at 18 weeks to have it checked again.  When should I push for cerclage?  Anyone ok on just progesterone ?