Rape, incest or life of momma ONLY.
I'm going to sound like an extremist, but I'm going to bring it up anyway.
Rape: Killing the child for the crimes of his or her father is not the answer. What if mother had a normal sex life with her husband and had been raped? What if they didn't know until the child was born who was the real father? Would it be OK to kill the child at 2 weeks old if it was determined that the rapist was the father? Why is it OK to kill the child earlier than that?
Incest: See Rape. Same deal.
Live of the Mother: What mother would not give up her own life to save her son or daughter? Who is to say with 100% accuracy that if a child is not aborted that the mother will die? What if the mother was dying and needed a vital organ that only her 1-year-old child could give her to save her life? Would it be OK to kill the child and take the organ to save the mother? Why is it OK to kill the unborn child to save the mother?
That being said, over 95% of all abortions committed in America are for matters of convenience - not rape, incest, or life of the mother. I'd be absolutely thrilled if we could eliminate that 95% - then we'll talk about the other 5% and whether those are a good idea or not.
and Incest? Why is this listed separately? When incest isn't rape, does the woman deserve some kind of special 'favor'?
Does the child who is the product of a rape or incest have less rights than one produced by consensual sex? In the case of a conception from rape or incest, the damage is already done to the mother, why compound her emotional problems by murdering the child?