Senator Tammy Duckworth, the Democratic senator from Illinois, gave birth to a baby girl, her office announced Monday. She is the first serving U.S. senator to have a baby.

She also happens to be 50.

“Bryan, Abigail and I couldn’t be happier to welcome little Maile Pearl as the newest addition to our family and we’re deeply honored that our good friend Senator (Daniel) Akaka was able to bless her name for us — his help in naming both of our daughters means he will always be with us,” Duckworth said in a statement.

Her announcement is part of a growing trend. The share of American women at the end of their childbearing years who have ever given birth was higher in 2016 than it was a decade earlier, reversing a near 40-year trend where fewer women in that age group were having babies.

Some 86% of women ages 40 to 44 were mothers in 2016, up from 80% in 2006, according to a recent analysis released of U.S. Census Bureau data by the Pew Research Center, a think tank in Washington, D.C.

This is Duckworth’s second child. She wrote on Twitter: “I’m hardly alone or unique as a working parent, and my daughter Abigail has only made me more committed to doing my job and standing up for hard-working families everywhere.” She’s not wrong.

“ There’s been a gradual increase in births for women in Tammy Duckworth’s age group (45 to 54) over the last decade. ”

“Not only are women more likely to be mothers than in the past, but they are having more children,” the report found. Overall, women have an average of 2.07 children during their lives — up from 1.86 in 2006, the lowest number on record. And among those who are mothers, family size has actually increased. In 2016, mothers at the end of their childbearing years had about 2.42 children, compared with a low of 2.31 in 2008.

“The Great Recession intensified this shift toward later motherhood, which has been driven in the longer term by increases in educational attainment and women’s labor force participation, as well as delays in marriage,” the Pew report found. “Given these social and cultural shifts, it seems likely that the postponement of childbearing will continue.”

There are health risks with having a baby in your mid- to late-40s. At 40, the chances of having a baby with Down Syndrome is 1 in 100. At 45, that risk rises to 1 in 30. Mothers in their 40s also have a higher rate of C-sections due to complications, low birth weight and stillborn babies. And the Centers for Disease Control and Prevention has reported a gradual increase in births for women in Duckworth’s age group (45 to 54) over the last decade.

“The recent rise in motherhood and fertility might seem to run counter to the notion that the U.S. is experiencing a post-recession ‘baby bust,’” Gretchen Livingston, a senior researcher at Pew, wrote in the report. Pew’s analysis is based on a cumulative measure of lifetime fertility (the number of births a woman has ever had) while reports of declining U.S. fertility are based on annual rates, which capture fertility at one point in time.

By that latter measure, however, fertility is still on a downward trajectory in the U.S. The St. Louis Federal Reserve reported 1.85 births per woman in 2015, down from 2.12 births per woman in 2007, but up from a low of 1.73 births per woman in 1976. However, those figures pale in comparison to 1960 when there were 3.65 births per woman.

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“ ‘Over the last 35 years, America’s fertility rate has reflected, to some extent, the business cycle.’ ” — - Federal Reserve Bank of Cleveland

Why the decline? Many families require two paychecks and must postpone buying a house — and starting a family — while they save for a down payment. Other women are delaying having a family to focus on their career and education. Child care remains one of the biggest household expense, according to Child Care Aware of America, a nonprofit group in Arlington, Va. The average cost of sending two children to day care outpaces median annual rent costs in all 50 states.

“Over the last 35 years, America’s fertility rate has reflected, to some extent, the business cycle,” a 2015 report by the Federal Reserve Bank of Cleveland stated. Between 2008 and 2013, the fertility rate of women with college degrees fell to 57 babies per 1,000 women from 64, and to 50 babies per 1,000 women from 57 for women without college degrees. Other studies have claimed pesticides on fruits and vegetables, may also complicate fertility.