(CNN) -- Americans are having fewer children.
One report says the number of births was so low in 2017 that it wasn't enough to keep the population levels steady.
The National Center for Health Statistics released its report Thursday.
The study finds that overall, the total fertility rate for the U.S. is 16 percent below what is considered the level needed for the population to replace itself.
According to researchers, the only states that are keeping up with the population are South Dakota and Utah.
They admit there were some limits to their report.
For example, the number of births actually used as the basis for calculating total fertility rate was small for some groups of women.