I'd need a lot more detail before I'd concede that they were "sequestering" those women.
If a pregnant women is caught using drugs, in some states she can be taken into protective custody so that she does not take any more to harm her child. She is also given a longer sentence than if she were not preganant, and the child can be taken away after birth.
I agree with you that it would be unreasonable to do something like this to a woman if she merely had a history of drug use.