The researchers found that for every 1,000 women aged 15-19 in 2016, there were 20.3 births — a 51 percent fall from 2007, when there were 41.5 births for every 1,000 women in that age group.
» RELATED: Celebrate declines in teen pregnancy
Since 1991, the rate among all teens has plummeted by two-thirds.
"Data [from previous years] really suggests it is access to contraceptives and use of contraceptives that has really led to these kind of changes," Elise Berlan, a physician specializing in adolescent medicine at Nationwide Children's Hospital, told CNN.
Berlan said most teens are using some form of birth control: condoms, withdrawal and the pill.
Unlike teens, however, the birth rate for women between the ages 30-34 increased last year and women ages 35-39 had their highest birth rate since 1962.
» RELATED: How well is Georgia caring for its children?
But overall, U.S. fertility rates still hit a historic low in 2016, the CDC and NCHS study found, largely due to fewer young women (teens and 20-somethings) giving birth.
And demographers are debating whether or not these declining fertility rates are leading the country toward a "national emergency," as some demographers have described, according to the Washington Post.
But some are still optimistic, citing lower fertility rates in other developed countries that have leveled off.
And, as the Washington Post points out, "as fertility treatments have extended the age of childbearing, the birthrates among women who are age 40 to 44 are also rising."
Read the full CDC and NCHS study.