Pregnant women who took epilepsy drug valproate were four times more likely to give birth to a baby with birth defects, a study has shown.
The medication is responsible for "severe malformations" in 2,150 to 4,100 children in France, according to a preliminary study by French health authorities.
Valproate - known in France under the brand name Depakine - has been on sale there since 1967; and in Britain under the name Epilim since 1973.
Sodium valproate is also prescribed under different brand names for people suffering from bipolar disorder.
The report, jointly issued by the French National Agency for the Safety of Medicines (ANSM) and the national health insurance administration, confirmed that the drug is "highly teratogenic", meaning that it can disturb the development of an embryo.
Birth defects attributed to the medication included spina bifida, which occurs 20 times more frequently in foetuses exposed to the medication, as well as defects of the heart and genital organs.
The risk of autism and developmental problems was also found to be higher and will be quantified in a follow-up report due later this year.
An earlier estimate suggested that 30 to 40% of children exposed in the womb could suffer such disorders.
While the report offers new findings, the health scandal is not new.
Last November there was a £10.7m settlement in France for people harmed by sodium valproate during pregnancy.
And UK support group Fetal Anti Convulsant Syndrome Association (FACS) has long been calling for doctors to tell their patients about the high risk that sodium valproate poses.
In January 2015, the UK Government warned that unborn children exposed to valproate were "at a high risk of serious development disorders".
However, the medication only began carrying warnings on its packaging in July 2016.
Following news of the settlement in France, FACS urged women who took valproate during pregnancy to register their child's name on its database.
In March, Sky News exposed a pregnancy drug cover-up , revealing how documents relating to the drug Primodos were destroyed and information withheld.