There are many reasons to despise George Dubbya Bush. The Toxic Texan has sabotaged ten years of negotiations that tried to tackle the world's greatest environmental threat, in order to help his political donors. He is threatening global security by ripping up a peace treaty, in pursuit of Star Wars fantasies.

But as he tries to joke away his global calumny during meetings in London and in Genoa (at the G8 summit), little is heard of what can only be called his most pernicious international act. On his first day in office, he introduced a policy that is promoting Aids, encouraging maternal deaths, and increasing poverty among the world's most vulnerable people.

To understand just how pernicious it gets, consider the story of the Nepalese girl Min Min Lama. At the age of 13, she was raped by an uncle. When it became obvious that she was pregnant, another relative drugged her and aborted her baby without consent. The police found the foetus and sentenced Min Min to 20 years in jail for killing an unborn baby. She was eventually released, but only after lobbying by the International Planned Parenthood Federation and the Family Planning Association of Nepal. Bush has now withdrawn all financial support for these organisations, and will do the same for any other charity which suggests that the punishment for abortion in Nepal should not be life imprisonment.

This is Bush's new policy on aid. It wasn't to please oil companies or the Dr Strangeloves of the Pentagon, but the religious right.

The change seemed innocuous enough at first. Bush declared that the US would not give money to charities that work in abortion-related activities or advocate a change in the law on abortion. US aid has not been spent directly on abortions or abortion counselling since 1974, but this has been taken a step further: no US funding will be given to charities that spend donations on abortion-related activities, even if the money comes from other sources. Any charity that receives US money now has to sign a "global gag" clause, promising that it will have nothing to do with abortion. The consequences are already felt: family planning and HIV-prevention charities have lost millions of dollars in funding, forcing them to close life- saving, poverty-reducing projects.

Pramilla Senanayake, the assistant director general of the International Planned Parenthood Federation, which is the world's largest sexual health charity, said: "Due to Bush's action, there will be more people dying of Aids. There will definitely be more abortions, rather than less, and maternal mortality will rise."

The federation, which refused to sign the global gag, spends 0.07 per cent of its total income on abortion-related activities and, as a result, lost $8m, or 8 per cent of its income. A drop-in centre in Lima, Peru, offering counselling and information to young people is due to close. A youth centre in Tirana, Albania, offering condoms and emergency contraception is under threat. A centre in Ghana which reaches out to disadvantaged girls to educate them about contraception is to shut.

The federation has also been working with drug addicts, helping them to avoid HIV. A project that offers needle exchange in Ukraine is being closed: thanks to Bush, more Ukrainians will get Aids. The project also helps women with contraception, in an attempt to tackle their dependence on abortion as a method of family planning. With less access to contraception, Ukrainian women will resort to more abortions.

In June, the federation was forced to shut the doors of three clinics in rural Nepal, which were offering voluntary sterilisation services to women who decided they had had enough children. Now, with no access to contraception, these women are left with a choice between having more children and resorting to illegal abortions.

All charities that work in the field are affected. Marie Stopes International has closed two centres in Kenya, after losing $1.6m of funding. The centres gave family-planning and HIV-prevention advice in the slums of Nairobi. Marie Stopes doesn't offer abortions in Kenya, but because it does so in Britain, Bush is punishing the slum-dwellers of Nairobi. Tony Kerridge of Marie Stopes said: "It's an unconscionable act by Bush, designed to placate fundamentalist right-wing opinion. They are making the most vulnerable women in the world suffer." Spacing babies is better for the mother's health, increases each baby's chance of survival, and is important in reducing family poverty.

Fertility in developing countries has halved in the past 50 years, but around 400 million couples still lack effective access to contraception. Around the world every year, 600,000 women - about one a minute - die from pregnancy-related causes, including 78,000 from unsafe abortions. Now Bush is hindering those who wish to help.

There are attempts to fight back. While Bush was in Europe, Nirmal Bista, head of the Family Planning Association of Nepal, gave evidence to a US Senate hearing on the impact of the new policy. But if Bush refuses to listen to the concerns of the world's richest countries, he is hardly likely to worry about those of its poorest.

Anthony Browne is health editor of the Observer, and a trustee of Population Concern