This is a really difficult question. It really depends on the child.
If I had a daughter that wasn't responsible, didn't even have a clue who the dad was, already skipped out on caring for pets, or neglected to maintain a C average in school, she'd likely have a PINS put on her, and yes, I'd likely try to have the fetus aborted if she didn't show actual efforts of doing a 180. It's wrong to make an unborn human suffer negligence simply so they will be born. I'd rather a crack addict get an abortion than either deliver a crack-addicted baby and put them up for adoption, or deliver a crack-addicted baby and abuse the child.
If they were responsible in every other right, just had a contraception bork or what-have-you, then I'd have to hear her out and what her plans are. If her plans are both reasonable, and seem feasible, then I'd let her have her choice, but would strongly suggest an adoption. If that was totally out of the question, I would offer my help during school or work hours, but I am not going to take care of a child that I didn't plan for, did not want, and is not mine all the time.
Let's say in this situation, my daughter maintained a C average or greater, didn't drink often(and vowed to not drink at all during pregnancy.), didn't smoke(Likewise, vowed to stop during pregnancy), didn't/doesn't/will not do drugs, and either had/has a job, or goes to summer school/gets their GED when discovering they are pregnant and want to keep the child.
Bonus points if she knows who the father is and he's willing to help in any minute way.
ON THE FLIPSIDE;
If my son(who I actually have.) got a girl pregnant within 9 to 15 years from now(ages 13-19) I would not let him ignore his child. At least, not let him do that and live with me. This is the only exception where I would help the mother as much as could, particularly if she is still in school.
I'm not sure how all the mechanics would work until such an event occurs, but I'd sure as ******** be pissed about it if he tried to play it off as he didn't have a son. ******** that, then I don't have a son.