I think they may be looking for IC Incomptent Cervix. I had it & it was discovered at 24 weeks because I was spotting. OB told me most people don't know they have IC until a few late term losses. I ended up on bedrest for the last 12 weeks of my pg. It was all worth it because I have a wonderful DD. GL
Warning
No formatter is installed for the format bbhtml
I had mine checked at 8, 12, 19 , and I will again at 22 weeks for any shortening and possible dilation from an incompetent cervix. I would guess they would be checking at 26 weeks for any possible changes and maybe to test for group b.
Re: Cervix checkup
That's very early unless you have a condition that would indicate your cervix needs to be checked.
Most doctors don't start internals until 36 or 37 weeks. Some never do them at all.