When she first became a mother, Melinda Pietrusza kept her job at an art gallery and took the baby to work with her. But after baby No. 2 came along, she decided to become a stay-at-home mom.

Now Pietrusza has four children ages 5 and under. She also has a lot more company in her decision to trade paid work for the unpaid kind than she would have had a decade ago.

An estimated 5.4 million mothers stayed home with their children last year, according to a new report from the U.S. Census Bureau. That's about 850,000 more than the number who did so 10 years earlier. And 88 percent of them said they made the choice primarily to care for children.

The bureau's report, its first-ever analysis of stay-at-home parents, found that more fathers stayed home as well -- 98,000 compared with 76,000 a decade ago. But only 16 percent said they were out of the labor force for child-care purposes. The rest cited illness or disability (45 percent), failure to find work, attending school or other reasons.

According to the survey, 20 percent of the stay-at-home moms lived in households earning $100,000 or more, while 2.3 percent were in households earning less than $10,000.