Providers of women’s healthcare around the world are preparing for potentially disastrous consequences should Donald Trump win the US presidential election in November.

Policies pursued during Trump’s last presidency caused “devastating” harm in a number of countries, said Beth Schlachter, a senior director at MSI Reproductive Choices in the US. It meant “clinics shuttered, health teams closed, women dying … but a second Trump term will be on a different scale”.

Global health charities lost US funding if they refused to agree not to “perform or actively promote abortion” under the “global gag rule”. This frequently meant the closure of facilities offering wider health services, such as family planning.

Joe Biden scrapped the ban in 2021 a week after he was inaugurated as US president in a move celebrated by health groups around the world. However, rightwing US strategists have set out detailed plans in their Project 2025 roadmap for a Republican administration to change the way the US government operates immediately after a Trump victory.

They are pushing for even wider restrictions on the activities of any organisation receiving US funding, the withdrawal of American support from international agencies, and the country’s influence to be used to further restrict access to abortions globally.

Schlachter said the sector needed “to get our heads around the implications of Trump retaking the White House”. Efforts by Trump to distance himself from Project 2025 were disingenuous, she suggested. “These are his people and they are telling us loud and clear the damage they intend to inflict.”

The global gag rule requiring organisations receiving US funding for family-planning services to agree not to perform or actively promote abortion has existed under Republican presidents since Ronald Reagan. The Trump administration went further, however, and made that agreement a condition for organisations to receive US funding for global healthcare in general.

The Project 2025 papers suggest the next Republican president should go further still and apply the gag rule “to all foreign assistance, including humanitarian aid”. This would affect about $51bn (£40bn) in overseas aid at current levels, health policy analysts suggest.

Such an expansion would be “huge and terrible”, said Dr Marleen Temmerman, a professor in obstetrics and gynaecology at the Aga Khan University East Africa and former director of reproductive health at the World Health Organization (WHO).

Under Trump’s last administration, US funding for research into subjects such as cardiovascular disease and diabetes was imperilled by the provision of abortions for foetal malformation at the university’s hospital, she said.

Dr Carole Sekimpi, the senior Africa director for MSI Reproductive Choices, said the 2017 gag rule was “disastrous for women”.

“If anything, it increases the number of abortions – because you have more and more women with limited access to contraception, limited access to information, and therefore with a higher likelihood of unplanned pregnancies, and therefore the need for an abortion,” she said.

The gag rule had a wider chilling effect, Sekimpi added. “It does really embolden the opposition. Those who are anti-rights, anti-choice – the hate movement.”

Temmerman said organisations would need to work together and potentially hive off work in reproductive healthcare into separate organisations to safeguard their other projects.

The US is responsible for almost two-thirds of global funding for sexual and reproductive health and rights promotion, according to a report by the German Foundation for World Population (DSW), a family-planning charity.

During the last Trump presidency, MSI saw annual donor income drop by $30m – or 17% – because it refused to sign the global gag rule. The charity said that meant 8 million women lost access to family-planning services – resulting in an estimated 6m unintended pregnancies, 1.8m unsafe abortions and 20,000 maternal deaths.

The Guttmacher Institute published a study looking at the impact in Uganda and Ethiopia, which found the global gag rule “stalled and even reversed progress toward expanded access to modern contraception”.

In Nepal, MSI had been working with the government to expand family-planning services, training health workers and establishing clinics.

“Everything changed after the election of Donald Trump,” said Tushar Niroula, operations director at MSI Nepal. “The operation had to be gradually closed down.”

The proportion of women of reproductive age in Nepal using modern contraceptives had stagnated, he said. “Underprivileged populations in hard-to-reach areas are not able to get the access to the services. That’s the effect of the global gag rule.”

Partner agencies were afraid to refer women to MSI for abortion care even in cases of rape, incest or where the mother’s life was at risk, which were all exceptions to the global gag rule, the charity said, adding that desperate women would opt for unsafe methods.

“It’s devastating,” Niroula said. “We have seen a lot of cases where women have opted for traditional methods of abortion and have got complications, and have nearly died.”

Documents published by Project 2025 suggest membership of international organisations such as the UN and WHO should be seen as only “a means to attain defined goals” and stress that withdrawal is an option “when such institutions act against US interests”.

The US should work with a coalition of “like-minded nations” to shape the work of international agencies, building on the anti-abortion Geneva Consensus Declaration signed by the last Trump administration and 33 largely illiberal or authoritarian governments, they suggest. The US rescinded its signature a few months afterwards after Trump left office.

Individuals linked to the last Trump administration and to Project 2025 are already working in countries including Guatemala and Uganda to embed policies based on that declaration, according to analysis by the reproductive rights group Ipas.