thanks for your query.
A cut off of 2.5 mm is considered critical as a predictor for preterm labour.
Please understand that this is measured by transvaginal sonography
, and a difference of few mm between observers is common, as it is pretty subjective.
However, at a length of 1 - 1.5 cm, preterm labour is imminent, and all the precautions given to you were rightly given.
At 3 cm, however, you need not have complete bed rest, or very rigorous precautions, but you need to be vigilant and careful, and have relative bedrest.
The weekly injections are given as progesterone
is a tocolytic
( prevents preterm labour ).
Cervical encirclage is rarely performed after 22 - 24 weeks, unless exceptional circumstances are there.
however, it is not indicated at present at the cervical length of 3 cm.
You still have a long way to go , as far as the pregnancy
is concerned, so you have to continue taking the medical advice
and hope for the best results.