The number of abortions in the United States has dropped to its lowest rate since abortion was legalized nationwide in 1973.

The abortion rate in 2014 (the most recent data available) was at 14.6 abortions per 1,000 women of childbearing age, 15-44 years old, according to a report released Tuesday by the Guttmacher Institute. That's a research group that supports legalized abortion. The institute surveyed known abortion providers in the country to come up with this data.

Not only is that the lowest abortion rate on record (they started keeping records following the landmark Supreme Court decision Roe v. Wade), but it's also a 14 percent decline in the abortion rate from 2011.

The number of abortions performed in the United States in 2014 dropped to 926,200,. That's down 12 percent from 2011 when 1.06 million abortions were performed. (Abortions peaked in 1990 at 1.6 million, The Associated Press reports.)

Abortion rate dropped in Minnesota, too

The report found there were 9,760 abortions performed in Minnesota in 2014. That's a 13 percent decline in the state's abortion rate between 2011 and 2014, from 10.7 to 9.3 abortions per 1,000 women of reproductive age.

The number of abortions in Minnesota represent about 1.1 percent of all abortions performed in the United States in 2014.

In 2014, there were 11 facilities in Minnesota that provided abortions (including six clinics). That's down from 2011, when there were 15 providers (seven clinics). And the report notes that some 95 percent of Minnesota counties don't have clinics that provide abortions.

Why the drop?

The report didn't investigate the why behind the declining abortion rate nationwide. But it did suggest improved use of birth control and an increase in abortion restrictions passed in some states contributed to the decline in abortions in some capacity. We'll break down these two ideas below.

Birth control

The increased availability of birth control through the Affordable Care Act – especially contraceptives such as IUDs – has contributed to the drop in unplanned pregnancies, the report said. This led to fewer women getting pregnant when they didn't want to, and in turn led to a decline in the number of abortions performed.

"[The report] shows that we're finally doing a better job of helping women get access to birth control that's affordable and that's high-quality," Cecile Richards, the president of Planned Parenthood, told NPR News.

Fewer clinics

The Guttmacher Institute also suggests it could be attributed to abortion restrictions passed on the state level in recent years, making it harder for women who want to get an abortion to do so in some states. But the report notes this probably didn't have as much of an impact on abortion decline as access to birth control did.

Some anti-abortion groups say the drop in the abortion rate shows these restrictions are working. Kristi Hamrick, a spokeswoman for Americans United for Life, told NPR News the regulations are having a "real, measurable impact on abortion."

But the Guttmacher Institute disagrees, saying restrictions likely contributed to abortion declines in some states, but can't explain the entire drop nationwide – more than 60 percent of the decline in abortions happened in states that didn't have new restrictions, the report explained.

Actions by the current Congress

The release of this report comes at a time when the Republican-controlled Congress is looking to defund Planned Parenthood and repeal the Affordable Care Act – both things women's health advocates argue have helped reduce the number of unplanned pregnancies in the United States by providing more affordable birth control options.

Vox explains more about Republicans efforts in this story.