The best essay I ever read concerning abortion was by the late Dr. Carl Sagan and his wife Ann Druyan. Originally published in Parade magazine, April 22, 1990 as "The Question of Abortion: A Search For Answers", and reprinted as Chapter 15 in his book "Billions and Billions".
The article asks the question "Can one be both pro-choice and pro-life" and looks at both sides of the subject in what I felt was a very fair manner, including the scriptural references which fundamentalists use to support their cause, and also including the scientific data available at the time the article was written.
In the early stages of development, there is very little to distinguish a fetus which will become a human from a fetus which will become any other vertebrate creature. Many people don't consider non-human creatures to be persons, so the question boils down to "when does the fetus become a person"? and the answer is "when uniquely human characteristics develop". The most human characteristic has nothing to do with the external form, but our brainwave patterns. Our brains are developed differently than even our closest genetic relatives, chimpanzees. Yet the brain doesn't show these distinct patterns until the 24th to 27th week of pregnancy, around the sixth month. Prior to that time, the fetus has some detectable brain activity, but it isn't different from what would be detected in any other vertebrate fetus.
From this, I gather that the soul hasn't moved in yet, because the vessel isn't ready to contain it. So if the decision is made to terminate the pregnancy, one isn't killing a soul, one is instead halting construction on the residence which would eventually be home to a soul. The soul which might have moved into that vessel will find another vessel instead. Should the decision to terminate be made after the 24th-27th week, the soul still would not die, but merely move out and find another vessel.
I strongly encourage anyone with questions about this topic to read chapter 15 of "Billions and Billions", as it provides what to me seems like a very rational and comforting viewpoint.