Short Cervix & Cerclage: Understanding Cervical Length Changes in Pregnancy

Question
I was diagnosed with a short cervix and had a preventative cerclage placed in December. I continue to get cervical checks for length. Until recently I held at my original measurement. Just prior to my last measurement I did not follow my peri's instructions and over did it, I have since been following docs orders closely. Is it possible that's why my cervix shortened? I am currently 30.2 wks pregnant. When does the cervix naturally start to shorten under the weight of the baby and in preparation for birth? At what point will my peri stop measuring my cervix? These bi-weekly measurements are very stressful. I dread my appointments and I'm very anxious for them to stop. Is it necessary to continue to measure my cervix this late in my pregnancy? I understand that as the baby grows he will not have as much space and will not move around quite as much, when does this usually happen? Also my baby has been measuring a couple of weeks ahead.   At my last appointment the babys head was measuring about 2 weeks ahead and estimated that he was weighting about 3 lbs. Is this normal? I've heard that u/s measurements are not as accurate the farther into pregnancy, is this true? If I do not go into labor shortly after or go past my due date after my cerclage removal at 36 weeks does that mean I really didn't suffer from IC and I didn't need all this additional measurements and stress? Thanks for taking the time to read and respond to my questions.  

Answer
HI Debi,
the cervix shortens and thins out right before labor. You need these measurement for more accuracy for your delivery and may last until then or til the ob is satisfied. Babies tend to settle down when in final position right before labor begins. Ultrasound is fairly accurate, but not 100%.