A woman doesn't. Unless it is an issue of rape (in which the child is still not guilty of any wrong doing in the matter), she is free to abstain in behavior that may result in a pregnancy.

I would also like to address the assumption that a number of children waiting for adoption is some kind of rebuttal. There will ALWAYS be children waiting for adoption. EVEN IF
EVERY child were matched up with a home or were taken in by someone
at this very moment, tomorrow would bring about another amount of children that would likewise be in need of adoption. And since there are procedures and screenings involved so that they aren't simply 'given' (thrown) to anyone or everyone regardless of requestor's behavior or intent, they will be "waiting for adoption" until the precautions protecting them are played out. After decades of use and millions of killed unborn, the implied claim that somehow abortion is an answer to the 'child waiting for a loving home' hasn't proven itself as 'the cure', now has it?