The women, all of whom suffer from epilepsy, conceived malformed foetuses after taking the drugs. Some were able to terminate the pregnancy, but others gave birth to babies with spina bifida, kidney defects and deformed limbs. In most cases, the women complain, they were never told by their doctor of the risks of taking the drugs in pregnancy.
Anti-convulsant drugs used to control epilepsy, such as Epilim and Tegretol, have been known since 1967 to carry a risk of birth defects. Department of Health and British Medical Association guidelines clearly state that, in almost all cases, doctors should discuss the risk of drug side-effects with patients.
Stephanie Moore, 27, is among 13 women whose cases are under legal investigation. In October 1990 she had her first pregnancy terminated at 20 weeks after discovering her unborn baby had spina bifida. She was taking large doses of Epilim and Tegretol and had not been told of any risk.
Mrs Moore, a solicitor's conveyancing clerk from Rotherham, South Yorkshire, was prescribed the drugs by a consultant neurologist when her epilepsy was diagnosed in 1988. 'Before I became pregnant, I visited my consultant with my husband and said we had decided to start a family. He just said it was fine,' Mrs Moore said.
The spina bifida was not discovered until late in the pregnancy and Mrs Moore decided to have an abortion. 'On the day I went in for the termination, I took my epilepsy tablets with me and put them on the bedside table.
'A young doctor, probably a trainee, came in and seemed rather horrified when she saw them. I can't remember her exact words, but I got the impression that I should not have been taking it.'
It was only later that Mrs Moore discovered that there was a known link between the drugs and birth defects. 'It is impossible to say now whether I would still have got pregnant if I had known. But I think I should have been told. The whole experience has been so upsetting that at the moment I don't feel I want children.'
Martin Brodie, director of the epilepsy research unit at Glasgow University, said the risk of anti-convulsants causing birth defects was well known, especially to epilepsy specialists. 'In my opinion, a doctor has got to discuss this with a patient. A woman who wants to become pregnant is entitled to have a say,' he said.
Dr Brodie pointed out that the risk of an abnormal pregnancy was small and had to be balanced against the possibility of an epileptic fit, which might lead to the death of mother or baby.
However, many epilepsy sufferers take a 'cocktail' of anti- convulsants which significantly increases the risks. If a pregnant woman is taking one anti-convulsant drug there is about a one-in-100 chance of a birth defect. If she is taking two different anti-convulsants the risk rises to six in 100; with three drugs it is one in 10, and with four drugs it is one in five. Twenty per cent of epileptics take more than one drug.
As well as spina bifida, recognised side-effects of anti-convulsants used in pregnancy include children born with congenital heart disease, cleft lip or palate, and malformations such as crooked fingers or odd features.
Guidelines issued by the Department of Health in 1990 say patients are entitled to information 'in a way they can understand' about proposed treatments, possible alternatives and any substantial risks, so they can make a balanced judgement. The British Medical Association and the Medical Defence Union, which represents doctors in legal actions, gives similar advice.
However, if any of the cases comes to court some doctors are expected to argue that they were right to withhold information because of the danger of causing stress and anxiety in pregnancy. A ruling by Lord Bridge in the House of Lords in 1985 also suggested that how much a doctor told a patient might be a matter of clinical judgement.
Sanofi, maker of Epilim, and other drug companies list the known side-effects of anti- convulsants in approved medical publications. In some cases, the makers print warnings on packets. New EC regulations will make it obligatory to include clear information sheets with drugs.
Ten solicitors representing the women have commissioned preliminary investigations from medical experts to establish if there is a prima-facie case against either the doctors or drug companies.