Elizabeth Renstrom for TIME
May 30, 2017 12:01 AM EDT

The rate at which American teenagers are giving birth has hit a new record low, while a higher rate of women are delaying childbearing and giving birth well into their 30s, according to new research.

The teen birth rate dropped 9% from 2013 to 2014, reveals the annual report published in the journal Pediatrics. This continues a historic decline and marks a 61% decrease since 1991, bringing the birth rate for women ages 15 to 19 down to 24.2 births per 1,000 women. The infant mortality rate also dropped 2.3% in 2014, reaching an all-time low of 5.82 infant deaths per 1,000 live births.

To reach these findings, researchers examined birth certificates, death certificates and reports of fetal death in all U.S. states for the most recent year available, which was 2014.

Among the youngest group measured, women ages 15 to 17, the birth rate declined 11% from 2013, and the rate for teens aged 18 to 19 dropped 7%.

Overall, the rate of U.S. births rose 1% from the previous year. As fewer young women are having children, the data also shows that women are increasingly becoming mothers at older ages. The birth rate for women ages 30 to 34 rose 3% from 2013 to 2014, going from 98.0 to 100.8 births per 1,000 women, according to the report. For those ages 35 to 39, the birth rate also rose 3% in 2014, and it rose 2% for women aged 40 to 44.

The last 15 years have seen a significant shift in the age at which women first give birth. The percent of first births to women 30 or older rose from 24% in 2000 to 30% in 2014, while first births to women under 20 dropped significantly from 23% in 2000 to 13% in 2014.

The percent of births to unmarried women also fell in 2014, and teenagers made up just 14% of those unmarried births—the lowest number ever recorded.

The report also found decreases in the number of C-sections and premature births. The overall death rate for children aged 1 to 19 did not change.

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Write to Abigail Abrams at abigail.abrams@time.com.

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