No more reasonable than sequestering a person caught attempting to hire a hitman.
What if she is a known drug addict or alcoholic? Would it not be reasonable to sequester her in order to prevent her from poisoning her child?
No; we do not currently sequester anyone for what they MIGHT do, so why would we start then?
We throw such people in jail for attempted murder.
No; we do not currently sequester anyone for what they MIGHT do, so why would we start then?
Actually, we do. Known durg addicts are often prohibited from engaging in activities that put other people in danger. A drug-addicted mother can have her children taken away by social services.
I have not thought through the possible unintended consequences of a policy of sequestering drug-addicted pregnant women, and then taking away their children after birth, but if such a policy would on net save lives, I would support it.