In addition to those listed by LaMarca, there are many Irish songs about unwanted pregnancy. One I like as well as any (for I don't really like any of them) is The Gentleman Soldier. It starts
There was a gentleman soldier At a sentry he did stand. He saluted a fair maid. Will you wait and have his hand? So boldy then he kissed her, And he passed it off as a joke. He drilled her up on the sentry box For drubbing the soldier's coat. . . . In the end, the gentleman soldier turns out to have a wife and three kids, and Molly "had a little malitia boy, and she didn't know his name."