Mothers with epilepsy who were prescribed the drug sodium valproate during their pregnancy, and gave birth to children with birth defects and learning disabilities as a result, are suing the NHS, it was reported last night.

Twenty parents have been granted legal aid to launch action for compensation against the health authorities for alleged negligence. Nina Roland, the solicitor for the families, has claimed that the women were not adequately treated during pregnancy.

Ms Roland was reported as saying: "We have expert medical evidence to show that these women were not advised of the risks they faced and were not always given appropriate medicine." Sodium valproate has been prescribed to epilepsy sufferers for more than three decades and is still routinely being given to women of childbearing age, although the risks were first documented in the Seventies and despite the wide availability of alternative treatments.

Lawyers believe that many other parents will also make claims for compensation. Hundreds of children are believed to have been affected.

Several studies have shown a high incidence of birth defects among children whose mothers had taken the drug. The possible defects include spina bifida and abnormalities of the face and head, such as cleft palates, as well as learning difficulties.