Yeah, in a technical sense Beach is right, I just took Tu to mean the overall picture that most unwanted pregnancies come from the poor.
I'm thinking the opposite though. Most unwanted pregnancies are those middle-class kids and up that don't want mommy, daddy, neighbors, etc., knowing about it.
If they're truly poor, more kids could mean more money and wanting more kids.
Who knows though, I haven't actually looked at any stats myself.