The rate of abortions in the United States has fallen to its lowest level since the landmark 1973 U.S. Supreme Court decision Roe v. Wade that legalized the procedure, according to a new report by the Guttmacher Institute.

The abortion rate declined to 14.6 abortions per 1,000 women between the ages 15 and 44, which is the lowest rate ever recorded. The abortion rate has declined by 14 percent since 2011.

The Guttmacher report concluded that multiple factors have contributed to the declining abortion rate, and the “relationship between abortion access … and abortion rates is not straightforward.”

Rachel Jones, senior research associate at Guttmacher and lead author of the study, told NPR that the data shows that both a decrease in unintended pregnancies and increased restrictions on abortion care access have affected the national abortion rate.

“If there are women in these highly restrictive states who want abortions but can’t get them because there aren’t any clinics that they can get to, and that’s why abortion’s going down, that’s not a good thing,” Jones said. “But we think the story that’s going on in a lot of situations, in a lot of states, is that fewer women are having unintended pregnancies and in turn fewer abortions, and that is actually a good story.”

Unintended pregnancy rates in the United States reached a 30-year low in 2011, according to an analysis by Guttmacher. Among women ages 15-to-44, the unintended pregnancy rate fell from 51 percent of all pregnancies in 2008 to 45 percent in 2011.

The teen birth rate has declined almost continuously over the past 20 years, according to the Office of Adolescent Health at the U.S. Department of Health and Human Services. The teen birth rate has declined from 61.8 births for every 1,000 adolescent females in 1991 to 24.2 births for every 1,000 adolescent females in 2014.

There has also been a marked increase in the usage of long-acting reversible contraceptives (LARCs), including intrauterine devices (IUDs), according an analysis by the Center for Disease Control. LARC use among women between the ages 15 and 24 increased nearly four-fold between 2002 and 2006-2010, from 0.6 percent to 2.3 percent. LARC use among that same demographic doubled between 2011 and 2015 to 5 percent.

The implementation of the Affordable Care Act (ACA), which lowered the cost of birth control, including IUDs, is partially responsible for that jump. Americans who used birth control pills saved $1.4 billion on the cost of contraception in 2013 after the implementation of the ACA, according to a report published in the policy journal Health Affairs.

A barrage of state-level anti-choice policies have forced many abortion clinics to close in recent years. At least 162 clinics that provide abortion services have either closed or stopped offering the procedure since 2011, according to a report by Bloomberg.

In 2016, 18 states enacted 50 new abortion restrictions, which brought the number of new abortion restrictions since 2010 to 338, according to an analysis by Guttmacher. These anti-choice laws account for 30 percent of the 1,142 abortion restrictions enacted by state legislatures since 1973.

Megan Donovan, senior policy manager at Guttmacher, said in a statement that restricting access to abortion care may force people to delay terminating a pregnancy or carry an unwanted pregnancy to term.

“Instead, we should focus on increasing access to the full range of contraceptive methods, as well as to abortion services,” Donovan said. “Empowering women to prevent unintended pregnancies and plan their families is both a human rights priority and smart public health policy.”