From the CFFC website: Will I be excommunicated if I have an abortion?
The official Canon Law of the church at the present time states that anyone who commits the sin of abortion automatically excommunicates herself from the church. To commit the sin of abortion, you have to think that an abortion in your case, with all the circumstances of your life and your pregnancy, is a sin against God. You then have to decide that you are going to do it anyway, thus going against your conscience.
The Catholic church officially teaches that the conscience of an individual is supreme. If you carefully examine your conscience and then decide that an abortion is the most moral act you can do at this time, you are not committing a sin. Therefore, you are not excommunicated. Nor need you tell it in confession since, in your case, abortion is not a sin.
The "Liturgy for Seeking Wisdom" on the same page may be the most ludicrous thing I've ever seen.