Inpatient abortions and other reproductive health services prohibited by Catholic hospitals’ religious directives are being performed significantly less often as more Catholic-affiliated hospitals open, according to a new study.

The National Bureau of Economic Research examined Catholic hospitals across six states and found per-bed annual rates of inpatient abortions dropped by 30%. Rates of sterilization via tubal ligation also decreased by 31%.

“We find statistically significant reductions in multiple procedures defined as prohibited by the UCCSB religious guidelines,” the study concluded. “Most concerning are large reductions in the number of tubal ligations performed in Catholic-owned hospitals.”

Debate over what health services a Catholic hospital should or should not be allowed to prohibit has grown in recent years as such providers have made up an ever-increasing share of the nation’s health system.

Since 2001, there have been 120 mergers between Catholic and non-Catholic health systems, resulting in a 22% increase in Catholic providers, according to the study. Today, Catholic hospitals make up more than 14% of the all acute care hospitals and one in six acute care hospital beds in the U.S.

A spokesman for the Catholic Healthcare Association of the United States, which represents more than 600 hospitals and 1,400 long-term care facilities across 50 states, declined a request for comment, stating that they had not yet reviewed the findings of the report.

Church doctrine forbids Catholic hospitals from performing medical procedures such as abortion, sterilization, in vitro fertilization, and providing artificial means of birth control, as stated within the U.S. Conference of Catholic Bishops’ “Ethical and Religious Directives for Catholic Health Care Services.”

The bureau’s study found such hospital directives disproportionately affect low-income women because they lack the resources to travel to other facilities. Women of color and those without a college education are also severely impacted by hospitals that follow such directives. Those populations are more likely to rely on sterilization as a primary means of birth control, according to the study.

“The report kind of substantiates concerns that certain women will be impacted more by the doctrine than others, and particularly those who have the least resources,” said Lori Freedman, an associate professor and medical sociologist with the University of California San Francisco’s research group, Advancing New Standards in Reproductive Health.

A big concern is a lack of transparency among Catholic hospitals, according to Freedman. She believes they could do more to inform patients about the services they are allowed and not allowed to provide under religious doctrine.

“I think it’s time for the field of obstetrics and gynecology and family practice to really take responsibility in educating their patients really early and often about where to get what they need,” Freedman said. “People who work in Catholic hospitals should have a program in place for referring their patients early to appropriate provider.”

But the issue of transparency becomes moot for those women who live in areas throughout the country where a Catholic hospital is the only provider for miles. Currently, 46 Catholic hospitals are identified by the CMS as being “sole community” providers, where the other nearest facility is 35 miles away or further and would take at least 45 minutes to travel to get to the nearest similar hospital.