(CNN) - In the 46 years since abortion was legalized nationwide, the country has never seen abortion rates this low.
But those decreases might have little to do with anti-abortion laws passed across the country in recent years, researchers say.
"The US abortion rate dropped to 13.5 abortions per 1,000 women aged 15--44 in 2017, the lowest rate recorded since abortion was legalized in 1973," the Guttmacher Institute said.
The research group conducts an abortion provider census every three years and spends about two years analyzing and aggregating the data.
The newly released information found that between 2011 and 2017:
-- The number of abortions fell by 196,000—a 19% decline from 1,058,000 abortions in 2011 to 862,000 abortions in 2017
-- The abortion rate (the number of abortions per 1,000 women aged 15--44) fell by about 20%, from 16.9 in 2011 to 13.5 in 2017
-- The abortion ratio (the number of abortions per 100 pregnancies ending in either abortion or live birth) fell about 13%, from 21.2 in 2011 to 18.4 in 2017.
Despite hundreds of new abortion restrictions across the country, those restrictions "were not the main driver of the decline in the US abortion rate between 2011 and 2017," Guttmacher said Wednesday.
"Rather, the decline in abortions appears to be related to declines in births and pregnancies overall."
Guttmacher said 32 states enacted 394 restrictions between 2011 and 2017, and the vast majority of those measures took effect. (In other words, most of those restrictions were not struck down in court.)
Yet "nearly every state had a lower abortion rate in 2017 than in 2011, regardless of whether it had restricted abortion access," Guttmacher said. "Several states with new restrictions actually had abortion rate increases."
In addition to the decline in abortions, the rate of live births dropped by 98,000 -- suggesting a decrease in pregnancies overall.
"One possible contributing factor is contraceptive access and use," Guttmacher said.
"Since 2011, contraception has become more accessible, as most private health insurance plans are now required by the Affordable Care Act (ACA) to cover contraceptives without out-of-pocket costs."
But even with the declines, "one in four women of reproductive age nationally will have an abortion in her lifetime," the institute said.