Since the historic Roe v. Wade U.S. Supreme Court decision in 1973, national abortion rates have hit their lowest point, a sing that contraception is more effective than ever at preventing unplanned pregnancy.

According to the Washington Post, a new research paper cited data from 2011, the most recent year that abortion statistics are available. Since the procedure was legalized in all 50 states, the rate of abortions in the U.S. has dropped to less than 17 of ever 1,000 women.

The rate is just slightly higher than it was in 1973. The paper, published by the pro-abortion-rights groups Guttmacher Institute, did not explore why the decline occurred, but observed an uptick in the use of different forms of birth control.

"The decline in abortions coincided with a steep national drop in overall pregnancy and birth rates," study lead author Rachel Jones said in a news release. "Contraceptive use improved during this period, as more women and couples were using highly effective long-acting reversible contraceptive methods, such as the IUD. Moreover, the recent recession led many women and couples to want to avoid or delay pregnancy and childbearing."

The study authors noted that a slew of recent state laws banning abortion did not have an effect since those laws were only passed after 2011. Also a factor was the harsh economy, which caused couples to strictly follow their birth control regimen.

"Clearly, the availability of medication abortion does not lead women to have more abortions," Jones said in the release. "However, it has likely helped women obtain abortion care earlier in pregnancy, as evidenced by a shift toward very early abortions."

According to the study, CNN reported, abortion providers declined by four percent between 2008 and 2011. Even though states like Arkansas, Oklahoma, Idaho, Kansas and Vermont only lost one clinic that loss could have led to a lot less abortions the study authors said.

Gathering this kind of data was no easy task, the Washington Post reported, because abortion providers do not have to report their figures. Guttmacher mailed a census to all providers then followed up directly by phone with those who did not return the questionnaire.