A new Centers for Disease Control and Prevention report says the nation's general fertility rate dropped to an all-time low last year.
The rate - which measures the number of live births per 1,000 women - recorded a two-percent decline.
Other studies show the fertility rate has been dropping for a while.
And it's now at the level where the nation cannot replace its existing population.
Among other findings by the CDC, the birth rate among teenagers is declining - while the rate of early-term births is growing.