An expert on law and ethics yesterday expressed her fear that advances in genetic screening could ultimately lead to women being denied the choice to have children.

Professor Sheila McLean of the University of Glasgow's department of law and ethics in medicine said: ''One of the subjects that concerns me is that the increase in genetic knowledge will lead to an increase in screening in pregnancy and even pre-pregnancy,'' she said at a conference in Aberdeen organised by Aberdeen University and the Church of Scotland to discuss issues raised by genetic engineering.

The conference also heard of the threat to universities' abilities to benefit commercially from their research work in this field because of a possible global ''patent war''.

Professor McLean said pregnancy or pre-prgnancy screening posed a very stark set of choices for people in terms of their reproductive liberties.

''There are actually some circumstances in which the provision of additional information does not enhance choice, it makes people's choices constrained,'' she said.

''There is a certain weight now being given to concepts like inter-generational justice which is basically that you should not knowingly pass on dilatatory genes to the next generation, which means, for women in particular who have spent the last 100 years fighting for some kind of reproductive liberty, the chances are the state, or any kind of pressure, might constrain their freedom to make decisions.''

She cited the example of a case in the US where a woman discovered the foetus she was carrying had the gene for cystic fibrosis and her insurance company said to her they would pay for an abortion but would not pay for any health-care costs associated with her going through with the pregnancy. ''She did go through with the pregnancy and threatened to sue them and they backed down, but they won't always back down,'' she said. ''You can see the possibility of governments saying that you shouldn't have had that child because it has a particular condition.

''I think the biggest ethical difficulties we have at the moment, and potentially legal ones, are what it is we are trying to do when we screen.

It is quite clear that everyone wants to have a healthy child, but when we get to the stage of screening becoming effectively mandatory, or people are judged for having made their ''wrong'' decision,that is of real concern.

''The old-fashioned standard codes of medical ethics are not able to cope with the demands placed on them by genetics, so I think a new ethic is going to be needed to help doctors through this.''

Professor McLean said responsible and informed debate was required to obtain a more rational response to genetics to allow efficient regulation which will allow the reaping of the benefits that will come from genetic knowledge.

''My plea is we stop reading the Boys from Brazil and treating it as though it were serious, stop panicking over Dolly my favourite sheep and actually start considering the reality of what is possible and contemplating whether or not we want it to happen.''

She said the possibility of a patent war with countries offering tighter and tighter controls to entice pharmaceutical companies posed a potential problem.

The BMA was concerned that the financial gain from genetic development might drive scientists down paths they might not otherwise have explored.

''Whoever gets economic control of genetic information is going to be extremely rich and extremely powerful. Some estimates suggest that the pharmaceutical and biotechnology companies will be making half again what they are currently making in profits just on gentically based products. There is a huge, huge industry out there which stands to gain a great deal.

''As higher education becomes less well funded the scientist who wants to do what was called pure research is the scientist who will not get funding.

''Scientists will find themselves driven by commercial enterprises because that is the only way they will get fiunding to do research that may or may not lead to a product.

''There is a danger scientists will be pushed into certain lines, certain kinds of questions, which will almost certainly be the questions that affect the rich world because that's where the biggest markets will be even though 80% of human genetic material belongs to the Thirld World.''

The same fears were expressed by Professor Michael Steel of the Univesity of St Andrews medical science department.

He said there was a very delicate balance to be struck.

''The danger is that patents will cover so much,'' he said. ''The moment a drug company discovers a gene, a mutation, they patent the mutation and that is protected for a number of years and they can develop drugs based on that knowledge.

''What they would like to do is patent the whole bit of DNA that contains that gene, and preferably patent all of the proteins that interact with that.

The more widely they can cast the patent net ,the more complete protection they have and the more money is going to come in the next 50 years out of this development. The danger is the university that wants to work on some other aspect of this discovery they have made will never be able to benefit in commercial terms. The patent laws could become so wide that everything is protected.''