Are Buddhists against abortion?

While other religions seem to have a definition position on abortion I've never come across the Buddhist view on this. From a naive perspective I would imagine that Buddhists would be prolife rather then prochoice - the abstain from killing precept seems to be the relevant one. But I would imagine it would also depend on when Buddhist believe that life begins or becomes sentient. Is there any pointers to the ethics of abortion in the scriptures (pali canon, mahayana etc..) or perhaps guidance/opinions from more contemporary teachers. I feel that the real position could be quite nuanced. Many thanks for any/all thoughts