I know such a study (or more than one) was done at least a decade back. I think I read the article in NYTimes magazine while flying to Chicago. As you might suspect, the birth rate for highly educated, well employed women was low. Marriage rate was also low compared to other females with less education and income. Lowest birthrate and least likely to marry were well educated, high income black women. They cited the reason as lack of husband material. Education level made the largest impact on a woman choosing to have children or not. More education equalled less kids.