I think it helps to think about it as organ donation - a person is donating their womb to the child like a person is donating a kidney. You can live with only one kidney, so theoretically would it be murder to not donate that kidney if you were the only available person for someone with severe kidney disease? It's only rhetorical and yes is a completely valid answer there.

But one important part of that is that even if you were donating a kidney and were on the operation table and changed your mind - in my mind the doctor should not then tie you down and forcibly remove your kidney as to not condemn the life of the recipient. In my mind, you are effectively donating a womb to that fetus during pregnancy, and a the responsibility of a person not donating an organ is not murder, even if it would be the morally correct thing to do.