NEW YORK (Reuters) - The number of births in the United States fell by 2% in 2023 from the previous year, driven in part by a marked birth rate decline among older teenagers and women aged 20-24, according to a report from the CDC released on Thursday.

The number of births in the U.S. fell to 3,591,328 in 2023 from 3,667,758 the year prior, according to provisional National Centers for Health Statistics (NCHS) data from the U.S. Centers for Disease Control and Prevention.

The decline puts the U.S. back on trend with the 2% decline seen in 2015-2020. In 2021, births rose 1%. The birth rate in 2022 was flat with the prior year.

Among women aged 25-34 years, who accounted for more than 2 million births in 2023, the birth rate fell about 2.5%, while births among women aged 20-24 years fell by 4% to a record low rate.

U.S. birth rates for teenagers aged 18-19 years fell 3%, also a record low, while the rate among teenagers aged 15-17 years was flat. Teen births have been falling since 2007.

"The decline in (teenage) birth rates has been quite phenomenal," Dr. Brady Hamilton, co-author of the report, said in an interview.

"For younger teens, it still has more to go in terms of decline," he said. "These are young women who are in the process of acquiring an education and preparing for the future."

Births declined for all races except Native Hawaiian and Pacific Islander women, for whom the number of births was basically flat. Black and Native American women experienced the largest birth declines, by 4% and 5%, respectively.

For women of Hispanic origin, births rose by 1%.

There was an uptick in deliveries by cesarean section last year, tracking with the rising average age of mothers, co-author Michelle Osterman, a health statistician at NCHS said.

The rate of infants delivered by cesarean section rose moderately for the fourth-consecutive year to 32.4%, the highest since 2013, up from 32.1% in 2022, the report said.

"We do know that older women tend to more have difficulties during delivering so it could be influenced by the increase in maternal age," said Osterman. "And 'low-risk' (cesarean) doesn't necessarily mean that it's not medically significant."

(Reporting by Amina Niasse; editing by Caroline Humer and Michael Erman)

By Amina Niasse