It really shouldn't matter. What matters is he believes life begins at conception, which is a reasonable position to hold, not to mention a mainstream position to hold. The awareness that life is happening inside there is intuitive to most couples who've been through pregnancy and anybody can observe that by watching a typical pregnant couple. It can also be observed through the emotional turmoil and regret that woman who've undergone abortions commonly live with. Beyond that, uncertainty should be enough to lead one to the default position of protecting it as human life. And once that premise is established, the decisions about "exceptions" for ending it should be easy to follow.