By Adam Brimelow
BBC Radio Health Correspondent
Women who took epilepsy medication while pregnant are suing for damages, claiming the drug harmed their children.
The drug is taken to prevent seizures in the brain
They have foetal anti-convulsant syndrome (FACS), which can involve physical and learning difficulties.
Lawyers argue the women had to choose between taking the sodium valproate risking side effects - and not, risking seizures.
Sanofi-Synthelabo, which makes the drug, said the risks associated with the drug were well-known to doctors.
It says there could be a range of causes for the congenital abnormalities, not just exposure to anti epileptic drugs during pregnancy.
The case is unusual because, rather than accusing the companies of negligence, the families are bringing their case under consumer protection laws introduced after the thalidomide scandal so that patients had a way of claiming compensation, even if negligence on the part of the drug company could not be proved.
The women's solicitor, David Body, said patients with epilepsy hoping to become pregnant were faced with an "impossible dilemma".
He said: "They have to make a choice between not taking the drug during pregnancy to protect the child, or alternatively running the risk of the syndrome by taking the drug".
It is accepted that the drug, marketed under the trade names Epilim or Orlept, is an effective treatment for epilepsy.
Deborah Mann's daughters Ronwen, aged 10, and her sister Branwyn, nine, both have the syndrome.
Mrs Mann, of Watford, Hertfordshrie, was put on sodium valproate as a child, and continued to take it during her pregnancy to control her epilepsy.
She says she is certain her children's disabilities were caused by the drug -- although the manufacturers dispute her claim.
Since the girls were born, they have also developed diabetes and asthma.
Deborah is one of the women who is suing for damages.
She says she is worried about her children's future.
"I'm not superwoman. I can't do everything for the girls. Not being there would be the worst scenario. I don't know what's going to happen."
Stringent medical tests
The BBC has learned that three cases have been filed at the High Court.
At least twenty more are pending, and there are hundreds of children with FACS who may be affected, although the precise figure is unknown.
David Chadwick, professor of neurology at the University of Liverpool, said: "For each individual woman there is a balance of risks between reducing the risk from drugs, but also reducing the risk that seizures carry to pregnancy.
"So it's a question of choosing the right drug for the right woman with epilepsy."
He said sodium valproate was linked with a 10% risk of foetal abnormalities if taken during pregnancy, compared to a four to five per cent risk with other anti-epileptic drugs, and a two to three per cent risk in babies generally.
In a statement, Sanofi-Synthelabo, who market sodium valproate under the trade name Epilim, said "Anti-epileptic drugs are crucial to the health of those prescribed them and have passed stringent medical tests".
It acknowledged an increased incidence of congenital abnormalities in children born to mothers with epilepsy who take anti-epileptic drugs during pregnancy , and said this risk was well known to doctors.
"Sanofi Synthelabo Ltd has at all times acted responsibly in relation to its marketing of anti-epileptic drugs", it said.