Yes, it's a difficult decision. We were told that the foetus was fully formed at three months which would be about 13 weeks. From then on it's physical development.
Whilst we're on the subject, I hear people saying that they got pregnant accidentally. Do me a favour.
(My mother always says that I was a mistake. The surgeon had told her that she wouldn't have any more children and then I came along about 6 years later when she was thirty. My younger sister followed when she was 36.)