Highly Educated, Older Women Having More Children

The researchers used data gathered by the June Current Population Survey, compiled by the U.S. Bureau of Labor Statistics and U.S. Census Bureau. The researchers also used the Vital Statistics Birth Data from the National Center for Health Statistics as a second data set.

She says it is still too early to be certain how or why the increase is happening, but the research clearly shows fertility rising for older, highly educated women since the 1990s. (Fertility is defined as the number of children a woman has had.) Childlessness also declined by roughly 5 percent between 1998 and 2008.

Because of the timing of the shift, the researchers think fertility treatments may have played a role.

"The data does not include information about whether women used fertility treatment," Shang said. "But we use the trends in plural birth rates to impute the share of the increase in fertility among highly educated women that is attributed to fertility treatment."

But, Shang said the study shows that fertility could have increased even in the absence of fertility treatments. The study did not directly address the causes of increased fertility in this group, but "we did list some possible explanations based on previous research," Shang said.

These include possible lessons from previous generations, an increased supply of personal services that have reduced childcare expenses, and the possibility of additional help from men taking more responsibility for child care.

The researchers couldn't say whether women are opting for families instead of their careers or in addition to their careers. "We know these women are opting for families," said Shang. "We don't know if they in turn are opting out of the labor market."

The study was published online April 23 in the Journal of Population Economics and will appear in an upcoming print issue.