Does the fact that a fetus can survive outside the womb prove their is pre-existance before a birth?

The whole abortion is all about religion. The odd thing is that abortion is not mentioned as a sin in the bible even though it was widely practiced in those days and long before Christ. I would like someone to explain that to me, I mean abortion was going on even during the Cleopatra days, before Christ. If it was truly an issue, wouldn't it say so in the bible? Maybe they literally felt that life began at birth in those days and maybe for some reasons Christians don't want to accept that?