Considering most women don't know they are pregnant until a missed period. If they take a pregnancy test on the first day of the missed period they are already 4 weeks pregnant. If they have irregular periods the chances are they could already be 6 weeks before they realise that there is a chance they might be pregnant. So a 6 week cut off time would be impossible. Women seeking illegal abortions would increase resulting in higher risk of injury and even death.
While I don't agree with abortion just for abortions sake (ie just plain careless when having sex) I do understand that for some women its their only option. I'm sure none of them enjoy the choice they make.
I think that the limit for an abortion on a healthy foetus should be 12 weeks. After that abortion should only be considered if they discover a severe abnormality at the 18 week ultrasound examination. I think 20-22 weeks should be the maximum limit then. Anything over that time period a partial birth abortion would have to be performed which is pretty much murder... legal due to government choices.