The sweeping new anti-abortion policy signed by President Donald Trump Monday may have the opposite effect to what’s intended, leading to many more abortions, aid groups say.

It could also mean more young women will die in childbirth, and years of progress in fighting HIV will be lost, they said.

People take part in a march demanding Dominican President Danilo Medina reviews the penal code and not approve the criminalization of abortion, in Santo Domingo, Dominican Republic, on Dec. 18, 2016. ERIKA SANTELICES / AFP - Getty Images

"No matter what the risk or barrier, women will continue to seek ways to end pregnancies and they will continue to needlessly die if safe abortion care is not accessible. The Trump Administration needs to face these facts and end policies that endanger the lives of women and girls," said Jason Cone, executive director of MSF-USA, also known as Doctors Without Borders.

Trump’s executive order reinstates and expands a Reagan-era policy often referred to as the "Mexico City Policy" or the "Global Gag Rule." It forbids giving federal funding to any foreign organization that performs abortions or, in many cases, that even mentions them as an option to women.

"Research over the past decade has shown that policies that ban medical providers from educating women about abortion and their family planning options—including birth control and condoms—actually lead to more unwanted pregnancies, more unsafe abortions and death, and higher rates of sexually transmitted diseases, such as HIV," said Cone, whose group gets no U.S. federal funding and will not be affected by the policy.

The rule has been turned on and off by various administrations for more than 30 years. Former President Barack Obama lifted it with one of his first executive orders.

Under former president George W. Bush, the rule applied to family planning groups. But Trump’s executive order expands it to all U.S. federal foreign health aid.

Related: What Will Trump Presidency Mean for Women's Health Abroad?

“I direct the Secretary of State, in coordination with the Secretary of Health and Human Services, to the extent allowable by law, to implement a plan to extend the requirements of the reinstated Memorandum to global health assistance furnished by all departments or agencies,” Trump’s order reads.

It’s bad news for groups who said they’d made a lot of progress in getting family planning help to millions of women around the world. And they predict it will backfire as millions or hundreds of millions of dollars in U.S. aid is pulled away from groups working across the globe.

“The enactment of the Global Gag Rule will cut off much-needed U.S. funds to international providers of family planning,” said Serena Jiwani of the United Nations Foundation.

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“When the policy was last enacted under President Bush, health care clinics in many countries were forced to close and outreach services for the hardest to reach populations were eliminated, leaving many of the world’s poorest people without access to critical services, such as maternal and child health care, HIV testing and counseling, and contraceptives, including condoms.”

This group just made it more difficult for women to get access to health care worldwide. You tell me what's wrong with this picture. pic.twitter.com/8UQFWg8qO3 — Kamala Harris (@KamalaHarris) January 23, 2017

The groups that provide these services get cash from many different sources, not just the U.S., and have longstanding programs that are not easily changed. Many operate in countries where abortion is legal and it can be impossible to separate operations that involve or mention abortion.

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“Trump’s Global Gag Rule will only lead to increases in unintended pregnancies, unsafe abortions, maternal and newborn deaths. This harmful policy undermines American democratic values of free-speech and imposes an anti-woman agenda,” saidNancy Northup, president and CEO of the Center for Reproductive Rights.

Anti-abortion-rights groups welcomed the new order.

"This is a welcome step toward restoring and enforcing important federal policies that respect the most fundamental human right—the right to life—as well as the long-standing, bi-partisan consensus against forcing Americans to participate in the violent act of abortion," said the U.S. Conference of Catholic Bishops.

“Trump’s Global Gag Rule will only lead to increases in unintended pregnancies, unsafe abortions, maternal and newborn deaths."

The rule will apply to programs funded by the U.S. Agency for International Development (USAID), the Centers for Disease Control and Prevention, National Institutes of Health, other Health and Human Services Department agencies, the Peace Corps, the Department of Defense and the U.S. President’s Emergency Plan for AIDS Relief (PEPFAR).

Because the Gag Rule has been reinstated and then revoked multiple times, many groups have real-world experience on what happens. “By cutting off funding for family planning, there is actually in increase in unintended pregnancies which actually leads to an increase in abortions,” said Seema Jalan, executive director of the Universal Access Project.

“When the gag rule was last in place under the Bush administration, it had profound implications, particularly for the poorest girls and women around the world,” Jalan said.

“Some of the most important providers of family planning services end up losing their U.S .funding for even their work on family planning, on maternal health, HIV testing and counseling, provision of contraceptives, et cetera. So we see the poorest girls and women around the world losing their access to basic health care.”

It doesn’t matter that the groups already may not use the U.S. money to provide or counsel about abortions, the experts note. They will now lose all funding if they are involved in any way.

“Included in that group are some of the largest providers of family planning services globally,” Jalan told NBC News.

"We see the poorest girls and women around the world losing their access to basic health care.”

It affects both married and unmarried women, many who do not have a say in whether they have sex. Family planning services allow them some measure of control over whether they get pregnant, however, Jalan said.

And a giant body of evidence shows that when women are able to delay childbearing, and to have fewer children, they are more likely to get educated and to help their communities grow economically.

It’s especially troubling with the epidemic of Zika virus that directly affects pregnant women. The virus can cause severe and profound birth defects, and women in areas where the virus is spreading need access to birth control, experts said.

Related: Abortion Could Be Outlawed in 33 States

“This is an unprecedented move, and the most extreme executive action we’ve seen of its kind,” said Katanya Mapp Frett, executive director of Planned Parenthood Global.

“The Global Gag rule as it existed under previous anti-women's health presidents was deeply harmful. But this action will be catastrophic for all communities, especially those relying on U.S. funding to address HIV/AIDS and maternal health care, and the fight against Zika.”

The Guttmacher Institute, which does research on reproductive health issues, said abortion rates have stalled in developing countries even as they’ve fallen in developed countries.

A study funded by the institute last year found that a quarter of all pregnancies worldwide end in abortion. “Our findings indicate that in many developing regions, women lack the contraceptive services they need and are unable to prevent pregnancies they do not want to have,” said Guttmacher researcher Gilda Sedgh.