Abort it or have it (there are issues for both subjects).
There is no way to get a woman un-pregnant. Abortion would be the only way, but abortion is killing the fetus. I believe that, unless the woman is at risk of losing her life, she should have her baby.
Go to Amazon.com and order a time machine. If you go back into the past and talk to your former self you can undo the situation or have a threesome. Your choice. While you're at it, undo this question.