In this case, given that you had a clear cause to which to attribute your bleeding, and given that no uterine bleeding would be expected at this time, you may treat this bleeding as dam makkah, blood from a wound. Dam makkah does not make a woman niddah. You need not observe any strictures of niddah, unless you were to have bleeding inconsistent with what is typical for cerclage.

We wish you well for the remainder of your pregnancy. BeSha'ah tovah!