(CNN) The general fertility rate in the United States continued to decline last year, according to a new report from the US Centers for Disease Control and Prevention's National Center for Health Statistics.
"The 2018 general fertility rate fell to another all-time low for the United States," the researchers wrote in the report, published Wednesday.
The report found that the general fertility rate dropped 2% between 2017 and 2018 among girls and women age 15 to 44 nationwide.
In 2017, the total fertility rate for the United States continued to dip below what's needed for the population to replace itself, according to a separate report published by the National Center for Health Statistics in January.
America's fertility rate and the number of births nationwide have been on the decline in recent years. A report of provisional birth data published by the National Center for Health Statistics in May showed the number of births last year dropping to its lowest level in about three decades.
Now the center's latest report presents selected highlights from that 2018 birth data.
For the report, researchers examined birth certificate data from the National Vital Statistics System's Natality Data File, taking a close look at births among white, black and Hispanic women in 2018.
When examined by race, the data showed that fertility rates declined 2% for white and black women, and 3% for Hispanic women, between 2017 and 2018.
The data also showed that the teen birth rate, for ages 15 to 19, fell 7% from 2017 to 2018. When examined by race, the data showed that teen births declined by 4% for black teenagers, and 8% for white and Hispanic teens.
Also among all births, the percentage delivered at less than full term, or 39 weeks, increased -- with preterm births climbing from 9.93% of births in 2017 to 10.02% in 2018, and early-term births rising from 26% in 2017 to 26.53% in 2018.
The percentages of births delivered at full-, late- and post-term declined, according to the data. Full-term births were down from 57.49% of births in 2017 to 57.24% in 2018, the data showed, and post-term births declined from 6.58% to 6.2%.
Overall, a rise in preterm births might be linked with a rise in births among women in their late 30s and 40s, since a later maternal age is a risk factor, Dr. Rahul Gupta, chief medical and health officer for March of Dimes, a nonprofit focused on the health of mothers and babies, said in May. He was not involved in the new report.
"The continuing shift toward increased maternal age at first birth is something that does increase the risk. However, it does not fully explain the increase in the preterm birth rate. So that's one of the challenges here, I think, for the nation," he said. "There is a lot more work that needs to be done as the preterm birth rate continues to rise."