CNN -- More women are waiting longer to have their first child.
That's according to a new report from the National Center For Health Statistics at the Centers For Disease Control And Prevention.
Researchers looked at data from the past four decades.
They found the number of women aged 40 to 44 years old delivering their first child has more than doubled since 1990.
And, in 2012, there were more than nine times as many first births to women over the age of 35, compared to the 1970s.
The study's authors point out that there are pros and cons for women waiting to have children.
Older moms typically have more resources, including higher incomes and better education than younger first-time moms.
But women who have their first children after 35 are more likely to have health problems, as are their children.
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