In most cases, an abortion is terminating an unwanted pregnancy. Not because the mother wnats to kill the baby, but because she is not ready for a child, doesn't want a child, or some other reason.
Too many abortions have been carried out in back-alley clinics with unsafe methods and ignorant providers. Women have gotten terribly sick and died because of botched abortions.
A fetus has only been in the world for a few months while the mother has been in the world for years. Both would be missed should one of them die, but the mother would be leaving so much should she be lost.
Abortions, contrary to those who oppose it, actually does help children; it reduces the number of abused/neglected children; if the parents didn't want the baby and end up having it, they (the parents) would become frustrated by the fact that they had a child that they didn't intend to have, leading to neglect and abuse of the child. With abortion, the child won't have to endure the abuse.
Too many "oops" babies have been born and life made hard for the child and the parents; it's the contraceptive, abortion, or adoption.
The act of terminating the life of an offspring before it is developed enough to leave the womb. Wouldn't be such a big issue if the vast majority of people who undergo it didn't make the stupid decision of fucking without thinking ahead about the consequences, such as getting pregnant as a result.