Highly educated women are waiting longer to have children, according to a new U.S. Census comparison of 2000 and 2010 birth and population data.

In 2000, 83 percent of women aged 25 to 34 with less than a high school degree had children. But only 42 percent of women aged 25 to 34 with at least a bachelor's degree had children.

Fast forward a decade to 2010, when all of these women reached the 35 to 44 age range:

-- By this time, there was little change among the lowly educated women; 88 percent of them had children (only a 6 percentage point increase.)

--- But the share of highly educated women with children nearly doubled. Whereas only 42 percent of them had children in their younger years, 76 percent of them had children by their middle-aged years.

"Our findings show that a 'delayer boom' is under way, where highly educated women initially delay childbearing but are more likely to have children into their 30s," said Census Bureau demographer Kristy Krivickas.

However, the highly educated women did not "catch up" with other women in terms of the number of children they had. In 2010, women aged 35 to 44 without high school degrees had 2.5 children on average. Women aged 35 to 44 with at least bachelor's degrees had only 1.7 children, on average.

What the basic data doesn't address is the psychology behind the delayer boom. Are highly educated women making conscious decisions to delay having children? Or is it a natural and even subconscious consequence of their commitments to college and to high-paying careers?