TREATMENT during pregnancy for HIV positive women means that paediatric AIDS could soon be a thing of the past. It is hoped that up to 98 per cent of babies would be born free of infection if the mother is treated with a combination of drugs during pregnancy and labour.

So far in Ireland all babies born to mothers who have been treated have been healthy, according to Dr Karina Butler, consultant in paediatric infectious diseases at Our Lady's Hospital for Sick Children in Crumlin, Dublin.

"This is a time of great optimism. In the US and Europe it has been revolutionary with much lower rates of infection occurring. This is now a preventable disease. What we should be focusing on now is primary infection and stopping transmission from mother to the infant during pregnancy. With combination therapy we could bring transmission rates down to two per cent," says Dr Butler, who treats the 31 children in the State with the virus.

Since AIDS was identified in Ireland, approximately 130 children born with the virus have been identified. The majority of these went on to lose their antibodies to the virus. But seven have died from AIDS related illnesses - only one of those in the past five years.

Dr Butler believes the main priority now is to identify the pregnant women who are infected in order to offer them treatment so the baby will be born without infection.

"We are no longer talking about finding out for finding out's sake. If antenatal screening was a matter of course we could then offer treatment to those women identified. We truly have the opportunity to prevent infection in a child. This is so important, because as good as our treatments are now, we are nowhere near a cure for this." Without intervention there is a one in three chance that the baby will be born with HIV.

A HIV positive woman who knows that she is pregnant should go to a doctor as soon as possible, says Dr Butler. "I would talk to her about the issues involved in terms of the likelihood of transmission and the chance we have of reducing that. Of course there are a lot of unknowns, including the effects of the drugs on the foetus or what the effects of exposure to these agents inutero will be in 20 years time. However, we are balancing the hypothetical chance of adverse risk to the real chance of transmitting a lethal disease. Our numbers are not huge here, but to date any woman who has received therapy has had a baby born infection free.

Doctors are unsure about when is the best time to start treatment for a pregnant mother. Dr Butler believes it is inadvisable in the all important first trimester, but since some women are not aware of their pregnancy until after that time, the matter may not arise.

"You could stop treatment in the first three months but you risk the mother's viral load (the amount of virus in her blood) going up and jeopardising her own treatment. As it rises it increases the risk of transmission. However, most transmission from mother to baby appears to take place around delivery.

THIS is probably because the placenta acts as a good barrier. We try to give them medicine right through labour. We also give the babies the drug AZT for the first four weeks. Up to 80 per cent of babies who are infected probably only become infected during the actual delivery process when the baby is exposed to maternal blood and secretions. This is good because it gives us time beforehand in which to do something."

Blood tests are taken when the child is born, at six weeks and three months after that. "We are only able to tell at birth in a third of cases because the viral load would be so low since the baby would have just become infected. With current testing we would know in up to 95 per cent of cases whether or not the child was infected by the age of six months. To be able to say for definite takes longer. It can take up to 15 months for a child to lose a mother's antibodies. These children will have to be followed up to see if there are long term effects."

Dr Butler says that people often question why someone who is HIV positive wants to have a child. "Sometimes both parents are ill and perhaps they have an ill child, and another child who is not infected but obviously would be affected by everything that is going on. They want to produce another uninfected child for this child. With the treatment developments a lot of people who would not have considered having a child before are now thinking about it. But in the majority of cases these pregnancies we see are not planned."