(CNN) — The abortion rate in the US has fallen to its lowest level since Roe v. Wade legalized the procedure, a new reports finds.

The report, by the Guttmacher Institute, found the rate has declined to 14.6 abortions per 1,000 women of, what is considered, childbearing age (that’s 15 to 44). That’s the lowest rate recorded since the landmark Supreme Court decision in 1973.

Another notable finding: the annual number of abortions in the US has dropped to under 1 million for the first time since the mid-1970s. It reached its peak of more than 1.6 million abortions in 1990.

The survey, “Abortion Incidence and Service Availability in the United States, 2014,” was authored by Rachel Jones and Jenna Jerman for the institute, which supports legalized abortion.

And even though the authors didn’t directly look at reasons for the decline, they attribute it to two contrasting developments: improved contraceptive use and a wave of abortions restrictions in several states.

The first has meant that women have been able to plan their pregnancies rather than need abortions, according to the survey.

The second has meant patients have to travel greater distances to access service.

“The majority of abortion patients — 75% — are poor or low-income, and nearly two-thirds are already parents. It can be very difficult for them to arrange for time off from work, transportation and child care,” said the study’s lead author Rachel Jones.

“While many find ways to access care despite these obstacles, some of the abortion rate decline is likely attributable to women who were prevented from accessing needed services.”

There’s a third interesting finding in the survey: there appeared to be no correlation between the number of clinics and abortion rates.

The number of clinics in the Midwest declined 22% during the study period, for instance, while the abortion rate in that region declined 9%.

In the Northeast, however, the number of clinics increased 14% and the abortion rate declined 11% between 2011 and 2014.