As the average age American women give birth has risen in recent years, new data suggest a similar trend in the United Kingdom. For the first time since the post-World War II baby boom, British women over age 40 are having more babies than women under 20, according to the Office for National Statistics (ONS).

The group found that, in 2015 in England and Wales, there were 15.2 births per 1,000 women ages 40 and over, compared to 14.5 per 1,000 women in their teens, BBC News reported. That year, there were 697,852 live births in the countries.

The number of teenage births in England and Wales has been on decline and is now down more than half from the 33 births per 1,000 women in 1990.

The average age British women give birth is now 30.3, a figure that has been on the rise since 1975, according to the ONS.

The group attributes this shift to advancements in fertility treatment, more women obtaining higher education, and changes in attitude around careers, as well as the rising costs of childbearing.

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Data suggested that women ages 30 to 34 have the highest fertility of any age group— 111 births per 1,000 women.

"While the risks should never be overplayed, men and women should be aware that reproductive outcomes are poorer in older women,” professor Adam Balen, chairmen of the British Fertility Society, told BBC News. "As well as it potentially taking longer to get pregnant, later maternity can involve a greater risk of miscarriage, a more complicated labor, and medical intervention at the birth."

In January, a report from the Centers for Disease Control and Prevention found that in the United States, the average age of women giving birth for the first time rose from 24.9 to 26.3 between 2000 and 2014. The report suggested that 9.1 percent of women having their first child were 35 or older.