Psalm 139 and Birth Control

A coworker and friend of mine, whose anonymity I shall maintain, has raised some interesting questions about the normative usage of Psalm 139 in arguments against abortion--that if they are true would they not also preclude birth control. I left my gut-shot answers, but the guy's got me thinking. They are some good questions. I'm most interested in the historical viewpoint on the subject. Check him out.