The bible says that until the age of cognitive reasoning (an age which can vary by individual) a human soul is pure and therefore goes to heaven by default.
I will never vote on the abortion issue in any legal forum (yes I have excuses not to vote on almost all issues). I can't fathom what it's like to be a girl, and I wouldn't presume to tell one how to use her own body. The pregnancy might be malignant to her own welfare. Perhaps she would be an unfit mother.
Surely God, in his infinite wisdom, would not damn a soul to hell for using the body He gave us to enjoy ourselves in unprotected fornication. Show me where in the bible it says 'no sex before marriage.' The ten commandments has a line: Covet not thy neighbor's wife, nor any of his property. Marriage is a bond between people, and the bible itself has only two references to it, both of them allegorical, comparing one's journey toward God to a marriage between a man and God.
John Calvin wrote that marriage is not a sacrament: it is neither holy nor of interest to God. Marriage is therefore a church and state affair. Writing those words may have set into motion the most cataclysmic series of religion-based law passings the LGBT community has ever faced in the form of USA legislature agin their lifestyle.
So if there's nothing in the bible about marriage, there can be nothing in the bible about sex outside of marriage (since the bible refuses to define marriage) and therefore it cannot be a sin to abort a child, since children are the inevitable result of sex. In fact, I suspect God foresaw our own technology reaching the point of puzzling out some of these mysteries.
I expect my great-grandchildren to live for several millenia, for example.
All this reasoning is probably flawed, but I'm standing behind it until I see the flaw. As far as I'm aware, the pro-lifers' objections would vanish if God appeared in the clouds and said, "It's O.K. to have abortions!"