(CNN) - The U.S. fertility rate has been dropping for years.
But new numbers show that it's now at the lowest rate it's been since the government starting keeping track in 1909.
The general fertility rate tells us how many children are being born into a given population during a specific period of time.
The National Center for Health Statistics analyzed birth certificates across the country.
Researchers found that, for women aged 15-to-44, there were 61.5 births for every thousand women during the year that ended in the first quarter of 2017.
That number represents a significant decline from the previous 12-month period.
Then, the rate was a whole percentage point higher, 62.5 births per one thousand women.
The report says the decrease is greater than what would be produced by pure chance.
But, U.S. fertility rates have been going down for years. They've been in steady decline since the baby boom that occurred after world war two.
At its height in 1957, the fertility rate in the United States was nearly double what it is now, 122.9 births for every thousand women.
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