The U.S. Census Bureau said an estimated 4.1 million U.S. moms will be celebrating the Mother's Day holiday with babies born during the past 12 months.
The data, released to mark the upcoming Mother's Day holiday, said 81 percent of women aged 40 to 44 in 2010 had given birth at least once, compared to 90 percent for the same age group in 1976.
The average age of women when they gave birth for the first time was 25.4 in 2010, up from 25.2 in 2009.
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