Full Idea
A fetus is not in jeopardy because it is in the womb, so an abortion originates the fatal sequence, and the mother is the agent. Hence Thomson's argument is invalid, and we must return to question of the moral status of the foetus.
Gist of Idea
The foetus is safe in the womb, so abortion initiates its death, with the mother as the agent.
Source
comment on Judith (Jarvis) Thomson (A Defense of Abortion [1971]) by Philippa Foot - Killing and Letting Die p.86
Book Reference
Foot,Philippa: 'Moral Dilemmas' [OUP 2002], p.87
A Reaction
The problem would be if a 'person' was safe, but only if I continue some sustained effort which is not required of me by normal duties.