Maybe a few, but most are consumed with paying taxes to support the children of those whose only ambition is pop out babies and collect welfare checks. Then the children of the welfare set take over the public schools (which are needless to say entirely financed by people who work and make a net contribution to the economy) and the taxpaying women realize they have to make even more money because they now have to pay for private school when they have children, unless they want their children "educated" in the government indoctrination centers and growing up regarding drug use, adolescent pregnancy, and general irresponsibility as normal.
Neither.
Paying taxes isn't a likely deterrent to pregnancy -- especially since income witholding makes it essentially invisible and painless.
Further, it doesn't take being "consumed with ambition."
What probably is true, is simply this: women, like men, tend to find their careers rewarding. Having a choice between children and careers means that some -- perhaps a lot -- of women will choose to continue their career for a while, figuring that childbearing will still be an option a few years hence.
The gall. If you're not born well-off, then just accept your lot and start cranking out the ankle-biters, mmmkay?