That's a separate issue from the citizenship of the child. I know well to do Mexicans, with no intent of ever living in the US, who come to the US to give birth, which they pay the bills for. They do it not for themselves, but in fear that Mexico might someday descend into left wing chaos (and it could happen if the current PRI candidate gets elected this year, rather than the PAN cannidate (PAN is Fox's party, and Fox is the first President not from PRI since the last revolution). They want their kids to have somewhere to go, their own fate is entirely secondary.
I don't think these were well to do women, but perhaps some were. From what I was told, they were not paying the bills.
susie