But that isn't true. Usually, this problem occured during childbirth prior to the advent of modern diagnostic technology and the modern C-section procedure. The choice then was to cut open the mother to save the child with great attendant risk to the life of the mother, or to crush the child's skull to kill it and possibly, but not in all circumstances, save the mother. That is the sort of choice I am referring to.
Nowadays, with the ability to naturally accelerate birth at the age of viability, and modern C-section procedures and the like, I can't think of a good reason to go in and directly kill a child to save a mother's life. And by directly kill a child I mean to use an abortion procedure to remove it from the womb, not for it to expire under cancer treatment or from removal of the fallopian tube in a ectopic pregnancy. Can you name a single mecial indication to use a direct abortion to kill an unborn child to save a mother's life?
Would you prefer that both die, rather than just one?
To go back to your different question, I'd say that it is better that two people die naturally then one from a murder. Simple notions of non-Marxian and non-Utilitarian/Consequentialist morality should tell you that.
Look at it this way, if you are standed on a desert island with your son and with no food, and knowing that a ship will come to pick you up in a month, could you licitly kill your child and eat him in order to survive that month? Would you prefer that one die from a murder, or both from starvation, knowing that the one to die is your own flesh and blood?