During a Fred Friendly hosted special on PBS, one of the pro-choice panelists tried to define abortion as a religious issue only to be confronted by Nat Hentoff defining himself as, I believe, an "Atheist Jew" and the spokesman from a pro-life organization telling her that he is agnostic. She couldn't handle that information so simply kept insisting that abortion was a religious issue despite having two people right in front of her giving her evidence that it wasn't.
While I believe in God and admire religious pro-life activists quite a bit, I think that using religious arguments against abortion isn't always helpful. If the person you are talking to is religious and generally shares your beliefs or if you are able to argue from the perspective of their beliefs, a religious argument can be very powerful. But if the person doesn't share your beliefs, then the person you are talking to can dismiss your abortion argument as a part of dismissing your religion. The argument will not be persuasive.
If you want to argue abortion from a religious standpoint, your first step must be to convince the person that your religious views are correct. If they refuse to accept them, then it will be impossible to discuss abortion based on shared religious beliefs. Don't even bother discussing abortion with them. You've already lost if your religion is the only argument you can bring to bear against abortion and you'll only add more ammunition to the argument that the pro-life position is only religious.