Drug trial to test HIV risk in pregnancy: Experimental results indicate benefit of AZT in preventing transmission to babies. Steve Connor reports

PREGNANT women in Britain are to take part in an international experiment to test whether AZT, the controversial anti-Aids drug, can prevent transmission of HIV to newborn infants.

Aids researchers are pressing the Department of Health to approve plans to give AZT to pregnant HIV-positive women despite fears that the drug may result in long-term side-effects in children.

Marie-Louise Newell, of the Institute of Child Health in London, said that researchers want to recruit between 2,500 and 3,000 volunteers for the Europe-wide trial. The experiment raises ethical questions because only about one in four babies born to HIV-positive women is infected with the virus. This means that three out of four babies will receive a potentially toxic drug for no reason.

Results of a similar but far smaller trial in the US and France showed that AZT - sold as zidovudine by the manufacturers Wellcome - can cut by two-thirds the transmission of the virus from mother to child.

James Balsey, of the Aids division of the US National Institutes of Health, briefed British scientists on the results of the American-led AZT trial at the Medical Research Council's annual meeting on Aids in Manchester, which ends today.

He said about 400 women took part in the experiment and those given AZT had a risk of transmission of about 8 per cent, compared with 25 per cent for those taking a placebo. The trial was stopped earlier this year because the US authorities deemed it unethical to continue prescribing the placebo.

The women and children suffered few, if any, side-effects, Dr Balsey said. 'There was nothing here we could attribute to the effect of the drug.' However, each child will be monitored for 21 years to see if there are any long- term effects.

Dr Balsey was asked by MRC researchers whether it was ethically acceptable to give a drug with known toxicity to pregnant women, many of whom may not have been fully aware of the long- term risks. He replied that there was extensive consulatation before the trial went ahead and the volunteers spent many weeks, or sometimes months, discussing the risk with trained counsellors.

Dr Newell said the ethics of a much bigger trial involving women in Britain are fraught with difficulties. 'We don't know the long-term effects on a child and it's very difficult to get informed consent. It's still a very difficult issue.' One fear is that AZT, which affects bone marrow cells, may increase the risk of childhood leukaemia. Despite the concern, some doctors in Britain are already prescribing AZT to pregnant HIV- positive women following the results of the American trial. 'Many clinicians have already started,' she said, although they are doing it on the basis that the drug may benefit the mothers rather than lessen the risk of HIV transmission.

In European countries, the risk of mother-to-child transmission is estimated to be in the region of 15 to 20 per cent, but can rise to 30 per cent in African countries.

Researchers at the Government's Public Health Laboratory Service estimate that between 255 and 273 babies in Britain were born to HIV-positive women in 1993.

In the Edinburgh region, one newborn baby in every thousand births is HIV-positive, compared with 1 in 570 in London and 1 in 9,000 in the UK as a whole. A study in which scientists tested blood samples anonymously from all newborn infants in Scotland revealed that out of 77 HIV-positive babies, only about half were known to local health authorities.