The percentage of U.S. women in their 30s and 40s who are childless is rising, new data from the U.S. Census Bureau show.

Some 15.3% of U.S. women aged 40 to 44 were childless in June 2014, up from 15.1% in 2012.

Changes in Census’s data processing likely affected its estimates for 2010 to 2012. But even before that, the trend was up: 9.6%...