Re: Thinning cervix
The number they look for is 3 - that is, 3cm in depth. My sis-in-law measured a 2.3 in an exam she had about 24 weeks, then three days later measured 1.8, and the doc put her on bed rest for the rest of her pregnancy. This is because if the cervix thins ("effaces") completely, the baby is in danger of being born... something that any OB looks for in exams in the last weeks of pregnancy is that degree of effacement, since it is an indicator of how close a woman is to labor, in addition to dilation. My sis-in-law has weekly cervical depth measurements now, and the measurement has gone up -- and down again-- since the initial diagnosis of a "short cervix". The shorter the measurement, the less activity she is supposed to have.... at the low end, she's confined to a reclining position except for breaks to eat, bathe, and go to the bathroom... she cannot even ride in the car as a passenger.
Because she was diagnosed close to her third trimester, circlage (where they sew the cervix shut until the baby is "fully baked") is not a possibility.
I should mention my sis-in-law's father is an OB as well, so she gets a very attentive second opinion on everything. He confirms that bed rest is the best approach. At 27 weeks, the baby is viable if born -- they just want to give the little one the chance to develop as much as possible before that happens. At 36 weeks, the restrictions ease up, as a baby born after that point is adequately developed and pretty much ready to be born.
Good luck to your daughter!