“And if it's the mother herself doing it, no I don't think she has a right to perpetrate such evil, just because it's "her body". And yes I would think it should be a criminal act.”
We do not criminalise women who smoke, take drugs, don’t eat an optimal diet etc To do so would be to take rights away from all women during pregnancy and genuinely reduce us to vessels.
I have known of a case where a woman was habitually consuming a poisonous/toxic substance during pregnancy, it was a pregnancy related psychological condition, she was sectioned until the birth, not for the harm she was doing to her baby but for the harm that she was doing to herself.
In UK law poisoning a pregnant woman would be prosecuted as a crime against the woman. The fœtus has no rights as a separate person.
In looking after the mother’s health, wellbeing and best interests the best interests of the fœtus are usually covered too, because their best interests are not truly separate. Mother and baby form a dyad. What is objectively good for the mother is good for the baby. If the mother is safe, well nourished, supported, content, relaxed all of that is going to be good for the baby too.
In the UK the combination of the rights being with the woman and not the foetus and the abortion laws we have create a reasonable balance.