This, in a nutshell. (See, not all nutshells are bad.)
As long as the baby can survive only in the mother's body, the mother's preferences rule, even though if someone else causes that baby to be harmed they can be held accountable. Much as the state cannot force a mother to give a kidney to her child, the state cannot force a mother to bring a child to term. I also agree that the health of the mother outweighs the health of the child, given proportionality. If the mother is at serious risk of dying or suffering grave physical damage, she should be free to have them take or destroy the baby at any stage. She should however not free to kill a baby because she is depressed.