In the space of 20 years, the number of graduates of the University of Pennsylvania's Wharton School who say they're likely to have children has ebbed by half.

Stew Friedman, director of the Wharton Work Life Project, says attitudes have changed for men and women both.

In 1992, almost 80 percent of the business school graduates said that they planned to have children. In 2012, that fell to just 42 percent.

"That is a pretty radical shift, what some are calling a 'baby bust,'" says Friedman.

Friedman believes the shift may be related to the graduates' expectations for the length of their work week. That estimate is way up.

Friedman says men and women have come closer on what it takes to have a two-career relationship. They have grown further apart on the issue of whether having a family will negatively affect their career. Women, he says,  have far more questions about whether they can "have it all."

"The extent to which attitudes have changed is greater for women with [...] a less sanguine view towards what's possible," he said.

The survey draws on answers from graduating Wharton students collected by the Work Life Project since 1991.