A report by the Guttmacher Institute released Wednesday outlines dramatic changes in the abortion landscape between 2011 and 2017. The U.S. abortion rate has again hit an all-time low. States passed an unprecedented wave of 400 bills imposing restrictions on the procedure, and medical abortions, which involve taking pills rather than undergoing a surgical procedure, became widely available.

The 48-page research document, used by policymakers and activists on both sides of the debate, provides detailed information by state and region about how American women access abortion.

There appears to be no clear pattern between efforts to ban or restrict abortion and the continuing decline in abortion rates, which has been ongoing for nearly 40 years. The declines were seen across regions and in states that are more supportive of abortion rights as well as those that are more restrictive.

“Antiabortion activists are going to try to take credit for this decline, but the facts don’t support their argument,” Rachel Jones, principal research scientist for Guttmacher, which supports abortion rights, said in a call with reporters.

The report estimated that the abortion rate in 2017, the most recent year studied, dropped to about 13.5 abortions per 1,000 women 15 to 44 years old. That compares with 14.6 in 2014 and 16.9 in 2011. It is the lowest rate since 1973, when the U.S. Supreme Court effectively legalized abortion nationwide through the landmark decision Roe v. Wade.

In total, 862,320 abortions took place in 2017 at health-care facilities. About 339,640 of those were medical abortions, which involve taking pills to induce miscarriage, as opposed to traditional surgical abortions.

Guttmacher said it was impossible to identify exactly what factors are driving the declines but pointed to fewer pregnancies, contraceptive access and use, a decline in sexual activity and infertility as possible causes. Researchers noted that it is possible that the drop is not as large as it appears due to a potential increase in self-managed abortion, which is not reflected in the data. Self-managed abortions are those that occur outside of health-care settings and might include the use of medication, herbs or other methods without the direct supervision of a medical professional.

Guttmacher noted that 32 states enacted restrictions during that time, such as waiting periods, parental consent for minors and ultrasound requirements. Nearly every state had lower abortion rates regardless of whether the state had passed any laws related to abortion access. Some states with new restrictions saw their abortion rates increase.

Guttmacher logged nearly 400 abortion restrictions passed by states from 2011 to 2017. Indiana, the home state of Vice President Pence, who served as governor there for four of those years, enacted the most at 37. Kansas was close behind with 31, and Arkansas enacted 29.

Many of the new restrictions have not gone into effect or have gone into effect temporarily because of court action. In April, for example, the Kansas Supreme Court blocked a law that banned the most common procedure for second-trimester abortions. It was the first state to try to stop this technique. And in July, a federal judge in Arkansas temporarily blocked three new abortion restrictions, including one that requires a physician performing an abortion to be board-certified, which probably would have resulted in the state’s only clinic having to close.

The U.S. Supreme Court in May went in the other direction, upholding part of a law signed by Pence that requires the fetal remains from an abortion to be buried or cremated.

Like many health-care studies, the data is a few years behind and does not include the effect of unprecedented state efforts this year to ban abortion at six weeks — in some cases, without exceptions for rape and incest. The data from 2017 also predates many efforts by the Trump administration, such as the changes to the Title X family planning program that prompted Planned Parenthood to refuse millions of dollars in funding.

The Guttmacher report provides a glimpse at how deep the divide has grown between states. Between 2011 and 2017, the number of clinics increased in the Northeast and the West but declined in the Midwest and the South.

Every state in the United States is home to an abortion clinic, but five — North Dakota, Kentucky, Mississippi, West Virginia and Kansas — had just one at the time of the report. (The situation has changed somewhat since then. Kansas now has four abortion providers and Missouri has one.) By contrast, California had 161 in 2017, the most in the nation. New York had 113, Florida had 65 and New Jersey had 41.

The change in abortion rates shows dramatic state-by-state variation. In Virginia, the abortion rate fell 41.5 percent, for example, while it ticked up slightly in New Jersey and the District.

Guttmacher officials emphasized that although restrictions may not be impacting the overall numbers, they take a toll on people.

“Abortion restrictions are coercive and cruel by design and intended to impose a heavy financial and emotional toll,” said Herminia Palacio, the Guttmacher Institute’s president and chief executive.

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